Locale (Java SE 26 & JDK 26)
Description: declaration: module: java.base, package: java.util, class: Locale
Keywords: java.util.Locale class

# Class Locale

java.lang.Object
java.util.Locale

All Implemented Interfaces:
  `Serializable, Cloneable`

public final class Locale extends Object implements Cloneable, Serializable
A `Locale` represents a specific geographical, political, or cultural region. An API that requires a `Locale` to perform its task is locale-sensitive and uses the `Locale` to tailor information for the user. These locale-sensitive APIs are principally in the java.text and java.util packages. For example, displaying a number is a locale-sensitive operation— the number should be formatted according to the customs and conventions of the user's native country, region, or culture.

The `Locale` class implements IETF BCP 47 which is composed of RFC 4647 "Matching of Language Tags" and RFC 5646 "Tags for Identifying Languages" with support for the LDML (UTS#35, "Unicode Locale Data Markup Language") BCP 47-compatible extensions for locale data exchange. Each `Locale` is associated with locale data which is provided by the Java runtime environment or any deployed `LocaleServiceProvider` implementations. The locale data provided by the Java runtime environment may vary by release.

## Locale Composition

A `Locale` is composed of the bolded fields described below; note that a `Locale` need not have all such fields. For example, `Locale.ENGLISH` is only comprised of the language field. In contrast, a `Locale` such as the one returned by `Locale.forLanguageTag("en-Latn-US-POSIX-u-nu-latn")` would be comprised of all the fields below. This particular `Locale` would represent English in the United States using the Latin script and numerics for use in POSIX environments.

`Locale` implements IETF BCP 47 and any deviations should be observed by the comments prefixed by "BCP 47 deviation:". RFC 5646 combines subtags from various ISO (639, 3166, 15924) standards which are also included in the composition of `Locale`. Additionally, the full list of valid codes for each field can be found in the IANA Language Subtag Registry (e.g. search for "Type: region").

language
  ISO 639 alpha-2/alpha-3 language code or a registered language subtag up to 8 alpha letters (for future enhancements). When a language has both an alpha-2 code and an alpha-3 code, the alpha-2 code must be used.
  Case convention: `language` is case insensitive, but `Locale` always canonicalizes to lower case.
  Syntax: Well-formed `language` values have the form `[a-zA-Z]{2,8}`.
  BCP 47 deviation: this is not the full BCP 47 language production, since it excludes extlang (as modern three-letter language codes are preferred).
  Example: "en" (English), "ja" (Japanese), "kok" (Konkani)
script
  ISO 15924 alpha-4 script code.
  Case convention: `script` is case insensitive, but `Locale` always canonicalizes to title case (the first letter is upper case and the rest of the letters are lower case).
  Syntax: Well-formed `script` values have the form `[a-zA-Z]{4}`
  Example: "Latn" (Latin), "Cyrl" (Cyrillic)
country (region)
  ISO 3166 alpha-2 country code or UN M.49 numeric-3 area code.
  Case convention: `country (region)` is case insensitive, but `Locale` always canonicalizes to upper case.
  Syntax: Well-formed `country (region)` values have the form `[a-zA-Z]{2} | [0-9]{3}`
  Example: "US" (United States), "FR" (France), "029" (Caribbean)
variant
  Any arbitrary value used to indicate a variation of a `Locale`. When multiple variants exist, they should be separated by `('_'|'-')`. Variants of higher importance should precede the others.
  BCP 47 deviation: BCP 47 subtags are strictly used to indicate additional variations that define a language or its dialects that are not covered by any combinations of language, script and region subtags. However, the variant field in `Locale` has historically been used for any kind of variation, not just language variations. For example, some supported variants available in Java SE Runtime Environments indicate alternative cultural behaviors such as calendar type or number script. In BCP 47, this kind of information which does not identify the language, is supported by extension subtags or private use subtags.
  Case convention: `variant` is case sensitive. BCP 47 deviation: BCP 47 treats the variant field as case insensitive.
  Syntax: Well-formed `variant` values have the form `SUBTAG (('_'|'-') SUBTAG)*` where `SUBTAG = [0-9][0-9a-zA-Z]{3} | [0-9a-zA-Z]{5,8}`.
  BCP 47 deviation: BCP 47 only uses hyphen ('-') as a delimiter, `Locale` is more lenient.
  Example: "polyton" (Polytonic Greek), "POSIX"
extensions
  A map from single character keys to string values, indicating extensions apart from language identification.
  BCP 47 deviation: The `extensions` in `Locale` implement the semantics and syntax of BCP 47 extension subtags and private use subtags. The `extensions` field cannot have empty values.
  Case convention: `extensions` are case insensitive, but `Locale` canonicalizes all extension keys and values to lower case.
  Syntax: Well-formed keys are single characters from the set `[0-9a-zA-Z]`. Well-formed values have the form `SUBTAG ('-' SUBTAG)*` where for the key 'x' `SUBTAG = [0-9a-zA-Z]{1,8}` and for other keys `SUBTAG = [0-9a-zA-Z]{2,8}` (that is, 'x' allows single-character subtags).
  Example: key="u"/value="ca-japanese" (Japanese Calendar), key="x"/value="java-1-7"

BCP 47 deviation: BCP47 defines the following two levels of conformance, "valid" and "well-formed". A valid tag requires that it is well-formed, its subtag values are registered in the IANA Language Subtag Registry, and it does not contain duplicate variant or extension singleton subtags. The `Locale` class does not enforce that subtags are registered in the Subtag Registry. `Locale.Builder` only checks if an individual field satisfies the syntactic requirement (is well-formed). When passed duplicate variants, `Builder` accepts and includes them. When passed duplicate extension singletons, `Builder` accepts but ignores the duplicate key and its associated value. Conversely, `Locale::of` and its overloads do not check if the input is well-formed at all.

### Unicode BCP 47 U Extension

UTS#35, "Unicode Locale Data Markup Language" defines optional attributes and keywords to override or refine the default behavior associated with a locale. A keyword is represented by a pair of key and type. For example, "nu-thai" indicates that Thai local digits (value:"thai") should be used for formatting numbers (key:"nu").

The keywords are mapped to a BCP 47 extension value using the extension key 'u' (`UNICODE_LOCALE_EXTENSION`). The above example, "nu-thai", becomes the extension "u-nu-thai".

Thus, when a `Locale` object contains Unicode locale attributes and keywords, `getExtension(UNICODE_LOCALE_EXTENSION)` will return a String representing this information, for example, "nu-thai". The `Locale` class also provides `getUnicodeLocaleAttributes()`, `getUnicodeLocaleKeys()`, and `getUnicodeLocaleType(String)` which provides access to the Unicode locale attributes and key/type pairs directly. When represented as a string, the Unicode Locale Extension lists attributes alphabetically, followed by key/type sequences with keys listed alphabetically (the order of subtags comprising a key's type is fixed when the type is defined)

A well-formed locale key has the form `[0-9a-zA-Z]{2}`. A well-formed locale type has the form `"" | [0-9a-zA-Z]{3,8} ('-' [0-9a-zA-Z]{3,8})*` (it can be empty, or a series of subtags 3-8 alphanums in length). A well-formed locale attribute has the form `[0-9a-zA-Z]{3,8}` (it is a single subtag with the same form as a locale type subtag). Duplicate locale attributes as well as locale keys do not convey meaning. For methods in `Locale` and `Locale.Builder` that accept extensions, occurrences of duplicate locale attributes as well as locale keys and their associated type are accepted but ignored.

The Unicode locale extension specifies optional behavior in locale-sensitive services. Although the LDML specification defines various keys and values, actual locale-sensitive service implementations in a Java Runtime Environment might not support any particular Unicode locale attributes or key/type pairs.

## Default Locale

The default Locale is provided for any locale-sensitive methods if no `Locale` is explicitly specified as an argument, such as `NumberFormat.getInstance()`. The default Locale is determined at startup of the Java runtime and established in the following three phases:

1. The locale-related system properties listed below are established from the host environment. Some system properties (except for `user.language`) may not have values from the host environment.

   Shows property keys and associated values
   Locale-related System Properties Key | Description
   --- | ---
   `user.language` | `language` for the default Locale, such as "en" (English)
   `user.script` | `script` for the default Locale, such as "Latn" (Latin)
   `user.country` | `country` for the default Locale, such as "US" (United States)
   `user.variant` | `variant` for the default Locale, such as "POSIX"
   `user.extensions` | `extensions` for the default Locale, such as "u-ca-japanese" (Japanese Calendar)

2. The values of these system properties can be overridden by values designated at startup time. If the overriding value of the `user.extensions` property is unparsable, it is ignored. The overriding values of other properties are not checked for syntax or validity and are used directly in the default Locale. (Typically, system property values can be provided using the `-D` command-line option of a launcher. For example, specifying `-Duser.extensions=foobarbaz` results in a default Locale with no extensions, while specifying `-Duser.language=foobarbaz` results in a default Locale whose language is "foobarbaz".)
3. The default `Locale` instance is constructed from the values of these system properties.

Altering the system property values with `System.setProperties(Properties)`/ `System.setProperty(String, String)` has no effect on the default Locale.

Once the default Locale is established, applications can query the default Locale with `getDefault()` and change it with `setDefault(Locale)`. If the default Locale is changed with `setDefault(Locale)`, the corresponding system properties are not altered. It is not recommended that applications read these system properties and parse or interpret them as their values may be out of date.

### Locale Category

There are finer-grained default Locales specific for each `Locale.Category`. These category specific default Locales can be queried by `getDefault(Category)`, and set by `setDefault(Category, Locale)`. Construction of these category specific default Locales are determined by the corresponding system properties, which consist of the base system properties as listed above, suffixed by either `".display"` or `".format"` depending on the category. For example, the value of the `user.language.display` system property will be used in the `language` part of the default Locale for the `Locale.Category.DISPLAY` category. In the absence of category specific system properties, the "category-less" system properties are used, such as `user.language` in the previous example.

## Obtaining a Locale

There are several ways to obtain a `Locale` object. It is advised against using the deprecated `Locale` constructors.

Locale Constants
  A number of convenient constants are provided that return `Locale` objects for commonly used locales. For example, `Locale.US` is the `Locale` object for the United States.
Factory Methods
  `Locale::of` and its overloads obtain a `Locale` object from the given `language`, `country`, and/or `variant`. `forLanguageTag(String)` obtains a `Locale` object for a well-formed BCP 47 language tag.
Builder
  `Locale.Builder` is used to construct a `Locale` object that conforms to BCP 47 syntax. Use a builder to enforce syntactic restrictions on the input.

The following invocations produce Locale objects that are all equivalent:

        Locale.US;
        Locale.of("en", "US");
        Locale.forLanguageTag("en-US");
        new Locale.Builder().setLanguage("en").setRegion("US").build();

## Usage Examples

Once a `Locale` is obtained, it can be queried for information about itself. For example, use `getCountry()` to get the country (or region) code and `getLanguage()` to get the language. `getDisplayCountry()` can be used to get the name of the country suitable for displaying to the user. Similarly, use `getDisplayLanguage()` to get the name of the language suitable for displaying to the user. The `getDisplayXXX` methods are themselves locale-sensitive and have two variants; one with an explicit locale parameter, and one without. The latter uses the default `DISPLAY` locale, so the following are equivalent :

        Locale.getDefault().getDisplayCountry();
        Locale.getDefault().getDisplayCountry(Locale.getDefault(Locale.Category.DISPLAY));

The Java Platform provides a number of classes that perform locale-sensitive operations. For example, the `NumberFormat` class formats numbers, currency, and percentages in a locale-sensitive manner. Classes such as `NumberFormat` have several factory methods for creating a default object of that type. These methods generally have two variants; one with an explicit locale parameter, and one without. The latter uses the default `FORMAT` locale, so the following are equivalent :

        NumberFormat.getCurrencyInstance();
        NumberFormat.getCurrencyInstance(Locale.getDefault(Locale.Category.FORMAT));

The following example demonstrates locale-sensitive currency and date related operations under different locales :

        var number = 1000;
        NumberFormat.getCurrencyInstance(Locale.US).format(number); // returns "$1,000.00"
        NumberFormat.getCurrencyInstance(Locale.JAPAN).format(number); // returns "¥1,000""
        var date = LocalDate.of(2024, 1, 1);
        DateTimeFormatter.ofLocalizedDate(FormatStyle.LONG).localizedBy(Locale.US).format(date); // returns "January 1, 2024"
        DateTimeFormatter.ofLocalizedDate(FormatStyle.LONG).localizedBy(Locale.JAPAN).format(date); // returns "2024年1月1日"

## Locale Matching

If an application is internationalized and provides localized resources for multiple locales, it sometimes needs to find one or more locales (or language tags) which meet each user's specific preferences. Note that the term "language tag" is used interchangeably with "locale" in the following locale matching documentation.

In order to match a user's preferred locales to a set of language tags, RFC 4647 Matching of Language Tags defines two mechanisms: filtering and lookup. Filtering is used to get all matching locales, whereas lookup is to select the best matching locale. Matching is done case-insensitively. These matching mechanisms are described in the following sections.

A user's preference is called a Language Priority List and is expressed as a list of language ranges. There are syntactically two types of language ranges: basic and extended. See `Locale.LanguageRange` for details.

### Filtering

The filtering operation returns all matching language tags. It is defined in RFC 4647 as follows: "In filtering, each language range represents the least specific language tag (that is, the language tag with the fewest number of subtags) that is an acceptable match. All the language tags in the matching set of tags will have an equal or greater number of subtags than the language range. Every non-wildcard subtag in the language range will appear in every one of the matching language tags."

There are two types of filtering: filtering for basic language ranges (called "basic filtering") and filtering for extended language ranges (called "extended filtering"). They may return different results by what kind of language ranges are included in the given Language Priority List. `Locale.FilteringMode` is a parameter to specify how filtering should be done.

### Lookup

The lookup operation returns the best matching language tags. It is defined in RFC 4647 as follows: "By contrast with filtering, each language range represents the most specific tag that is an acceptable match. The first matching tag found, according to the user's priority, is considered the closest match and is the item returned."

For example, if a Language Priority List consists of two language ranges, `"zh-Hant-TW"` and `"en-US"`, in prioritized order, lookup method progressively searches the language tags below in order to find the best matching language tag.

>        1. zh-Hant-TW
>        2. zh-Hant
>        3. zh
>        4. en-US
>        5. en

If there is a language tag which matches completely to a language range above, the language tag is returned.

`"*"` is the special language range, and it is ignored in lookup.

If multiple language tags match as a result of the subtag `'*'` included in a language range, the first matching language tag returned by an `Iterator` over a `Collection` of language tags is treated as the best matching one.

### Serialization

During serialization, writeObject writes all fields to the output stream, including extensions.

During deserialization, readResolve adds extensions as described in Special Cases, only for the two cases th_TH_TH and ja_JP_JP.

Implementation Note:

  ## Compatibility

  The following commentary is provided for apps that want to ensure interoperability with older releases of `Locale` provided by the reference implementation.

  ### Locale Behavior

  In order to maintain compatibility, Locale's (deprecated) constructors, `of(String, String, String)`, and its overloads retain their behavior prior to the Java Runtime Environment version 1.7. That is, a length constraint is not imposed on any of the input parameters. Similarly, the same preservation of past behavior is largely true for the `toString()` method. Apps that previously parsed the output of `toString()` into language, country, and variant fields can continue to do so (although this is strongly discouraged). A caveat is that the variant field will have additional information in it if script or extensions are present.

  In addition, BCP 47 imposes syntax restrictions that are not imposed by Locale's constructors. This means that conversions between some Locales and BCP 47 language tags cannot be made without losing information. Thus `toLanguageTag()` cannot represent the state of locales whose language, country, or variant do not conform to BCP 47.

  Because of these issues, it is recommended that apps migrate away from constructing non-conforming locales and use the `forLanguageTag(String)` and `Locale.Builder` APIs instead. Apps desiring a string representation of the complete locale can then always rely on `toLanguageTag()` for this purpose.

  ### Special cases

  For compatibility reasons, two non-conforming locales are treated as special cases. These are `ja_JP_JP` and `th_TH_TH`. These are ill-formed in BCP 47 since the variants are too short. To ease migration to BCP 47, these are treated specially during construction. These two cases (and only these) cause a constructor to generate an extension, all other values behave exactly as they did prior to Java 7.

  Java has used `ja_JP_JP` to represent Japanese as used in Japan together with the Japanese Imperial calendar. This is now representable using a Unicode locale extension, by specifying the Unicode locale key `ca` (for "calendar") and type `japanese`. When the Locale constructor is called with the arguments "ja", "JP", "JP", the extension "u-ca-japanese" is automatically added.

  Java has used `th_TH_TH` to represent Thai as used in Thailand together with Thai digits. This is also now representable using a Unicode locale extension, by specifying the Unicode locale key `nu` (for "number") and value `thai`. When the Locale constructor is called with the arguments "th", "TH", "TH", the extension "u-nu-thai" is automatically added.

  ### Legacy language codes

  Locale's constructors have always converted three language codes to their earlier, obsoleted forms: `he` maps to `iw`, `yi` maps to `ji`, and `id` maps to `in`. Since Java SE 17, this is no longer the case. Each language maps to its new form; `iw` maps to `he`, `ji` maps to `yi`, and `in` maps to `id`.

  For backwards compatible behavior, the system property `java.locale.useOldISOCodes` reverts the behavior back to that of before Java SE 17. If the system property is set to `true`, those three current language codes are mapped to their backward compatible forms. The property is only read at Java runtime startup and subsequent calls to `System.setProperty()` will have no effect. As of Java SE 25, the use of the `java.locale.useOldISOCodes` system property is deprecated. This backwards compatible behavior will be removed in a future release of the JDK.

  The APIs added in Java SE 7 map between the old and new language codes, maintaining the mapped codes internal to Locale (so that `getLanguage` and `toString` reflect the mapped code, which depends on the `java.locale.useOldISOCodes` system property), but using the new codes in the BCP 47 language tag APIs (so that `toLanguageTag` reflects the new one). This preserves the equivalence between Locales no matter which code or API is used to construct them. Java's default resource bundle lookup mechanism also implements this mapping, so that resources can be named using either convention, see `ResourceBundle.Control`.

Since:
  1.1
External Specifications
  - RFC 4647: Matching of Language Tags
  - RFC 5646: Tags for Identifying Languages
  - RFC 6067: BCP 47 Extension U
  - Unicode Locale Data Markup Language (LDML)
See Also:
  - `Locale.Builder`
  - `ResourceBundle`
  - `Format`
  - `NumberFormat`
  - `Collator`
  - Serialized Form

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `static final class`
  `Locale.Builder`
  `Builder` is used to build instances of `Locale` from values configured by the setters.
  `static enum`
  `Locale.Category`
  Enum for locale categories.
  `static enum`
  `Locale.FilteringMode`
  This enum provides constants to select a filtering mode for locale matching.
  `static enum`
  `Locale.IsoCountryCode`
  Enum for specifying the type defined in ISO 3166.
  `static final class`
  `Locale.LanguageRange`
  This class expresses a Language Range defined in RFC 4647 Matching of Language Tags.

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final Locale`
  `CANADA`
  Useful constant for country.
  `static final Locale`
  `CANADA_FRENCH`
  Useful constant for country.
  `static final Locale`
  `CHINA`
  Useful constant for country.
  `static final Locale`
  `CHINESE`
  Useful constant for language.
  `static final Locale`
  `ENGLISH`
  Useful constant for language.
  `static final Locale`
  `FRANCE`
  Useful constant for country.
  `static final Locale`
  `FRENCH`
  Useful constant for language.
  `static final Locale`
  `GERMAN`
  Useful constant for language.
  `static final Locale`
  `GERMANY`
  Useful constant for country.
  `static final Locale`
  `ITALIAN`
  Useful constant for language.
  `static final Locale`
  `ITALY`
  Useful constant for country.
  `static final Locale`
  `JAPAN`
  Useful constant for country.
  `static final Locale`
  `JAPANESE`
  Useful constant for language.
  `static final Locale`
  `KOREA`
  Useful constant for country.
  `static final Locale`
  `KOREAN`
  Useful constant for language.
  `static final Locale`
  `PRC`
  Useful constant for country.
  `static final char`
  `PRIVATE_USE_EXTENSION`
  The key for the private use extension ('x').
  `static final Locale`
  `ROOT`
  Useful constant for the root locale.
  `static final Locale`
  `SIMPLIFIED_CHINESE`
  Useful constant for language.
  `static final Locale`
  `TAIWAN`
  Useful constant for country.
  `static final Locale`
  `TRADITIONAL_CHINESE`
  Useful constant for language.
  `static final Locale`
  `UK`
  Useful constant for country.
  `static final char`
  `UNICODE_LOCALE_EXTENSION`
  The key for Unicode locale extension ('u').
  `static final Locale`
  `US`
  Useful constant for country.

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `Locale(String language)`
  Deprecated.
  Locale constructors have been deprecated.
  `Locale(String language, String country)`
  Deprecated.
  Locale constructors have been deprecated.
  `Locale(String language, String country, String variant)`
  Deprecated.
  Locale constructors have been deprecated.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `static Stream<Locale>`
  `availableLocales()`
  Returns a stream of available locales.
  `static String`
  `caseFoldLanguageTag(String languageTag)`
  Returns a case folded IETF BCP 47 language tag.
  `Object`
  `clone()`
  Overrides Cloneable.
  `boolean`
  `equals(Object obj)`
  Returns true if this Locale is equal to another object.
  `static List<Locale>`
  `filter(List<Locale.LanguageRange> priorityList, Collection<Locale> locales)`
  Returns a list of matching `Locale` instances using the filtering mechanism defined in RFC 4647.
  `static List<Locale>`
  `filter(List<Locale.LanguageRange> priorityList, Collection<Locale> locales, Locale.FilteringMode mode)`
  Returns a list of matching `Locale` instances using the filtering mechanism defined in RFC 4647.
  `static List<String>`
  `filterTags(List<Locale.LanguageRange> priorityList, Collection<String> tags)`
  Returns a list of matching languages tags using the basic filtering mechanism defined in RFC 4647.
  `static List<String>`
  `filterTags(List<Locale.LanguageRange> priorityList, Collection<String> tags, Locale.FilteringMode mode)`
  Returns a list of matching languages tags using the basic filtering mechanism defined in RFC 4647.
  `static Locale`
  `forLanguageTag(String languageTag)`
  Returns a locale for the specified IETF BCP 47 language tag string.
  `static Locale[]`
  `getAvailableLocales()`
  Returns an array of available locales.
  `String`
  `getCountry()`
  Returns the country/region code for this locale, which should either be the empty string, an uppercase ISO 3166 2-letter code, or a UN M.49 3-digit code.
  `static Locale`
  `getDefault()`
  Gets the current value of the `default locale` for this instance of the Java Virtual Machine.
  `static Locale`
  `getDefault(Locale.Category category)`
  Gets the current value of the `default locale` for the specified Category for this instance of the Java Virtual Machine.
  `final String`
  `getDisplayCountry()`
  Returns a name for the locale's country that is appropriate for display to the user.
  `String`
  `getDisplayCountry(Locale inLocale)`
  Returns a name for the locale's country that is appropriate for display to the user.
  `final String`
  `getDisplayLanguage()`
  Returns a name for the locale's language that is appropriate for display to the user.
  `String`
  `getDisplayLanguage(Locale inLocale)`
  Returns a name for the locale's language that is appropriate for display to the user.
  `final String`
  `getDisplayName()`
  Returns a name for the locale that is appropriate for display to the user.
  `String`
  `getDisplayName(Locale inLocale)`
  Returns a name for the locale that is appropriate for display to the user.
  `String`
  `getDisplayScript()`
  Returns a name for the locale's script that is appropriate for display to the user.
  `String`
  `getDisplayScript(Locale inLocale)`
  Returns a name for the locale's script that is appropriate for display to the user.
  `final String`
  `getDisplayVariant()`
  Returns a name for the locale's variant code that is appropriate for display to the user.
  `String`
  `getDisplayVariant(Locale inLocale)`
  Returns a name for the locale's variant code that is appropriate for display to the user.
  `String`
  `getExtension(char key)`
  Returns the extension (or private use) value associated with the specified key, or null if there is no extension associated with the key.
  `Set<Character>`
  `getExtensionKeys()`
  Returns the set of extension keys associated with this locale, or the empty set if it has no extensions.
  `String`
  `getISO3Country()`
  Returns a three-letter abbreviation of this locale's country.
  `String`
  `getISO3Language()`
  Returns a three-letter abbreviation of this locale's language.
  `static String[]`
  `getISOCountries()`
  Returns a list of all 2-letter country codes defined in ISO 3166.
  `static Set<String>`
  `getISOCountries(Locale.IsoCountryCode type)`
  Returns an unmodifiable `Set` of ISO3166 country codes for the specified type.
  `static String[]`
  `getISOLanguages()`
  Returns a list of all 2-letter language codes defined in ISO 639.
  `String`
  `getLanguage()`
  Returns the language code of this Locale.
  `String`
  `getScript()`
  Returns the script for this locale, which should either be the empty string or an ISO 15924 4-letter script code.
  `Set<String>`
  `getUnicodeLocaleAttributes()`
  Returns the set of unicode locale attributes associated with this locale, or the empty set if it has no attributes.
  `Set<String>`
  `getUnicodeLocaleKeys()`
  Returns the set of Unicode locale keys defined by this locale, or the empty set if this locale has none.
  `String`
  `getUnicodeLocaleType(String key)`
  Returns the Unicode locale type associated with the specified Unicode locale key for this locale.
  `String`
  `getVariant()`
  Returns the variant code for this locale.
  `boolean`
  `hasExtensions()`
  Returns `true` if this `Locale` has any extensions.
  `int`
  `hashCode()`
  Override hashCode.
  `static Locale`
  `lookup(List<Locale.LanguageRange> priorityList, Collection<Locale> locales)`
  Returns a `Locale` instance for the best-matching language tag using the lookup mechanism defined in RFC 4647.
  `static String`
  `lookupTag(List<Locale.LanguageRange> priorityList, Collection<String> tags)`
  Returns the best-matching language tag using the lookup mechanism defined in RFC 4647.
  `static Locale`
  `of(String language)`
  Obtains a locale from a language code.
  `static Locale`
  `of(String language, String country)`
  Obtains a locale from language and country.
  `static Locale`
  `of(String language, String country, String variant)`
  Obtains a locale from language, country and variant.
  `static void`
  `setDefault(Locale newLocale)`
  Sets the `default locale` for this instance of the Java Virtual Machine.
  `static void`
  `setDefault(Locale.Category category, Locale newLocale)`
  Sets the `default locale` for the specified Category for this instance of the Java Virtual Machine.
  `Locale`
  `stripExtensions()`
  Returns a copy of this `Locale` with no extensions.
  `String`
  `toLanguageTag()`
  Returns a well-formed IETF BCP 47 language tag representing this locale.
  `final String`
  `toString()`
  Returns a string representation of this `Locale` object, consisting of language, country, variant, script, and extensions as below: language + "_" + country + "_" + (variant + "_#" | "#") + script + "_" + extensions Language is always lower case, country is always upper case, script is always title case, and extensions are always lower case.

  ### Methods declared in class Object

  `finalize, getClass, notify, notifyAll, wait, wait, wait`
  Modifier and Type
  Method
  Description
  `protected void`
  `finalize()`
  Deprecated, for removal: This API element is subject to removal in a future version.
  Finalization is deprecated and subject to removal in a future release.
  `final Class<?>`
  `getClass()`
  Returns the runtime class of this `Object`.
  `final void`
  `notify()`
  Wakes up a single thread that is waiting on this object's monitor.
  `final void`
  `notifyAll()`
  Wakes up all threads that are waiting on this object's monitor.
  `final void`
  `wait()`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
  `final void`
  `wait(long timeoutMillis)`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
  `final void`
  `wait(long timeoutMillis, int nanos)`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

- ## Field Details

  - ### ENGLISH

    public static final Locale ENGLISH
    Useful constant for language.

  - ### FRENCH

    public static final Locale FRENCH
    Useful constant for language.

  - ### GERMAN

    public static final Locale GERMAN
    Useful constant for language.

  - ### ITALIAN

    public static final Locale ITALIAN
    Useful constant for language.

  - ### JAPANESE

    public static final Locale JAPANESE
    Useful constant for language.

  - ### KOREAN

    public static final Locale KOREAN
    Useful constant for language.

  - ### CHINESE

    public static final Locale CHINESE
    Useful constant for language.

  - ### SIMPLIFIED_CHINESE

    public static final Locale SIMPLIFIED_CHINESE
    Useful constant for language.

  - ### TRADITIONAL_CHINESE

    public static final Locale TRADITIONAL_CHINESE
    Useful constant for language.

  - ### FRANCE

    public static final Locale FRANCE
    Useful constant for country.

  - ### GERMANY

    public static final Locale GERMANY
    Useful constant for country.

  - ### ITALY

    public static final Locale ITALY
    Useful constant for country.

  - ### JAPAN

    public static final Locale JAPAN
    Useful constant for country.

  - ### KOREA

    public static final Locale KOREA
    Useful constant for country.

  - ### UK

    public static final Locale UK
    Useful constant for country.

  - ### US

    public static final Locale US
    Useful constant for country.

  - ### CANADA

    public static final Locale CANADA
    Useful constant for country.

  - ### CANADA_FRENCH

    public static final Locale CANADA_FRENCH
    Useful constant for country.

  - ### ROOT

    public static final Locale ROOT
    Useful constant for the root locale. The root locale is the locale whose language, country, and variant are empty ("") strings. This is regarded as the base locale of all locales, and is used as the language/country neutral locale for the locale sensitive operations.
    Since:
      1.6

  - ### CHINA

    public static final Locale CHINA
    Useful constant for country.

  - ### PRC

    public static final Locale PRC
    Useful constant for country.

  - ### TAIWAN

    public static final Locale TAIWAN
    Useful constant for country.

  - ### PRIVATE_USE_EXTENSION

    public static final char PRIVATE_USE_EXTENSION
    The key for the private use extension ('x').
    Since:
      1.7
    See Also:
      - `getExtension(char)`
      - `Locale.Builder.setExtension(char, String)`
      - Constant Field Values

  - ### UNICODE_LOCALE_EXTENSION

    public static final char UNICODE_LOCALE_EXTENSION
    The key for Unicode locale extension ('u').
    Since:
      1.7
    See Also:
      - `getExtension(char)`
      - `Locale.Builder.setExtension(char, String)`
      - Constant Field Values

- ## Constructor Details

  - ### Locale

    @Deprecated(since="19") public Locale(String language, String country, String variant)
    Deprecated.
    Locale constructors have been deprecated. See Obtaining a Locale for other options.
    Construct a locale from language, country and variant. This constructor normalizes the language value to lowercase and the country value to uppercase.
    Implementation Note:
      - Obsolete ISO 639 codes ("iw", "ji", and "in") are mapped to their current forms. See Legacy language codes for more information.
      - For backward compatibility reasons, this constructor does not make any syntactic checks on the input.
      - The two cases ("ja", "JP", "JP") and ("th", "TH", "TH") are handled specially, see Special Cases for more information.
    Parameters:
      `language` - An ISO 639 alpha-2 or alpha-3 language code, or a language subtag up to 8 characters in length. See the `Locale` class description about valid language values.
      `country` - An ISO 3166 alpha-2 country code or a UN M.49 numeric-3 area code. See the `Locale` class description about valid country values.
      `variant` - Any arbitrary value used to indicate a variation of a `Locale`. See the `Locale` class description for the details.
    Throws:
      `NullPointerException` - thrown if any argument is null.

  - ### Locale

    @Deprecated(since="19") public Locale(String language, String country)
    Deprecated.
    Locale constructors have been deprecated. See Obtaining a Locale for other options.
    Construct a locale from language and country. This constructor normalizes the language value to lowercase and the country value to uppercase.
    Implementation Note:
      - Obsolete ISO 639 codes ("iw", "ji", and "in") are mapped to their current forms. See Legacy language codes for more information.
      - For backward compatibility reasons, this constructor does not make any syntactic checks on the input.
    Parameters:
      `language` - An ISO 639 alpha-2 or alpha-3 language code, or a language subtag up to 8 characters in length. See the `Locale` class description about valid language values.
      `country` - An ISO 3166 alpha-2 country code or a UN M.49 numeric-3 area code. See the `Locale` class description about valid country values.
    Throws:
      `NullPointerException` - thrown if either argument is null.

  - ### Locale

    @Deprecated(since="19") public Locale(String language)
    Deprecated.
    Locale constructors have been deprecated. See Obtaining a Locale for other options.
    Construct a locale from a language code. This constructor normalizes the language value to lowercase.
    Implementation Note:
      - Obsolete ISO 639 codes ("iw", "ji", and "in") are mapped to their current forms. See Legacy language codes for more information.
      - For backward compatibility reasons, this constructor does not make any syntactic checks on the input.
    Parameters:
      `language` - An ISO 639 alpha-2 or alpha-3 language code, or a language subtag up to 8 characters in length. See the `Locale` class description about valid language values.
    Throws:
      `NullPointerException` - thrown if argument is null.
    Since:
      1.4

- ## Method Details

  - ### of

    public static Locale of(String language, String country, String variant)
    Obtains a locale from language, country and variant. This method normalizes the language value to lowercase and the country value to uppercase.
    Implementation Note:
      - This method does not make any syntactic checks on the input. Use `Locale.Builder` for full syntactic checks with BCP47.
      - The two cases ("ja", "JP", "JP") and ("th", "TH", "TH") are handled specially, see Special Cases for more information.
      - Obsolete ISO 639 codes ("iw", "ji", and "in") are mapped to their current forms. See Legacy language codes for more information.
    Parameters:
      `language` - A language code. See the `Locale` class description of language values.
      `country` - A country code. See the `Locale` class description of country values.
      `variant` - Any arbitrary value used to indicate a variation of a `Locale`. See the `Locale` class description of variant values.
    Returns:
      A `Locale` object
    Throws:
      `NullPointerException` - thrown if any argument is null.
    Since:
      19

  - ### of

    public static Locale of(String language, String country)
    Obtains a locale from language and country. This method normalizes the language value to lowercase and the country value to uppercase.
    Implementation Note:
      - This method does not make any syntactic checks on the input. Use `Locale.Builder` for full syntactic checks with BCP47.
      - Obsolete ISO 639 codes ("iw", "ji", and "in") are mapped to their current forms. See Legacy language codes for more information.
    Parameters:
      `language` - A language code. See the `Locale` class description of language values.
      `country` - A country code. See the `Locale` class description of country values.
    Returns:
      A `Locale` object
    Throws:
      `NullPointerException` - thrown if either argument is null.
    Since:
      19

  - ### of

    public static Locale of(String language)
    Obtains a locale from a language code. This method normalizes the language value to lowercase.
    Implementation Note:
      - This method does not make any syntactic checks on the input. Use `Locale.Builder` for full syntactic checks with BCP47.
      - Obsolete ISO 639 codes ("iw", "ji", and "in") are mapped to their current forms. See Legacy language codes for more information.
    Parameters:
      `language` - A language code. See the `Locale` class description of language values.
    Returns:
      A `Locale` object
    Throws:
      `NullPointerException` - thrown if argument is null.
    Since:
      19

  - ### getDefault

    public static Locale getDefault()
    Gets the current value of the `default locale` for this instance of the Java Virtual Machine.

    The Java Virtual Machine sets the default locale during startup based on the host environment. It is used by many locale-sensitive methods if no locale is explicitly specified. It can be changed using the `setDefault(Locale)` method.

    Returns:
      the default locale for this instance of the Java Virtual Machine

  - ### getDefault

    public static Locale getDefault(Locale.Category category)
    Gets the current value of the `default locale` for the specified Category for this instance of the Java Virtual Machine.

    The Java Virtual Machine sets the default locale during startup based on the host environment. It is used by many locale-sensitive methods if no locale is explicitly specified. It can be changed using the `setDefault(Locale.Category, Locale)` method.

    Parameters:
      `category` - the specified category to get the default locale
    Returns:
      the default locale for the specified Category for this instance of the Java Virtual Machine
    Throws:
      `NullPointerException` - if category is null
    Since:
      1.7
    See Also:
      - `setDefault(Locale.Category, Locale)`

  - ### setDefault

    public static void setDefault(Locale newLocale)
    Sets the `default locale` for this instance of the Java Virtual Machine. This does not affect the host locale.

    The Java Virtual Machine sets the default locale during startup based on the host environment. It is used by many locale-sensitive methods if no locale is explicitly specified.

    Since changing the default locale may affect many different areas of functionality, this method should only be used if the caller is prepared to reinitialize locale-sensitive code running within the same Java Virtual Machine.

    By setting the default locale with this method, all of the default locales for each Category are also set to the specified default locale.

    Parameters:
      `newLocale` - the new default locale
    Throws:
      `NullPointerException` - if `newLocale` is null

  - ### setDefault

    public static void setDefault(Locale.Category category, Locale newLocale)
    Sets the `default locale` for the specified Category for this instance of the Java Virtual Machine. This does not affect the host locale.

    The Java Virtual Machine sets the default locale during startup based on the host environment. It is used by many locale-sensitive methods if no locale is explicitly specified.

    Since changing the default locale may affect many different areas of functionality, this method should only be used if the caller is prepared to reinitialize locale-sensitive code running within the same Java Virtual Machine.

    Parameters:
      `category` - the specified category to set the default locale
      `newLocale` - the new default locale
    Throws:
      `NullPointerException` - if category and/or newLocale is null
    Since:
      1.7
    See Also:
      - `getDefault(Locale.Category)`

  - ### getAvailableLocales

    public static Locale[] getAvailableLocales()
    Returns an array of available locales. The returned array represents the union of locales supported by the Java runtime environment and by deployed `LocaleServiceProvider` implementations. At a minimum, the returned array must contain a `Locale` instance equal to `Locale.ROOT` and a `Locale` instance equal to `Locale.US`.
    Returns:
      an array of available locales

  - ### availableLocales

    public static Stream<Locale> availableLocales()
    Returns a stream of available locales. The returned stream represents the union of locales supported by the Java runtime environment and by deployed `LocaleServiceProvider` implementations. At a minimum, the returned stream must contain a `Locale` instance equal to `Locale.ROOT` and a `Locale` instance equal to `Locale.US`.
    Implementation Note:
      Unlike `getAvailableLocales()`, this method does not create a defensive copy of the Locale array.
    Returns:
      a stream of available locales
    Since:
      21

  - ### getISOCountries

    public static String[] getISOCountries()
    Returns a list of all 2-letter country codes defined in ISO 3166. Can be used to obtain Locales. This method is equivalent to `getISOCountries(Locale.IsoCountryCode type)` with `type` `Locale.IsoCountryCode.PART1_ALPHA2`.

    Note: The `Locale` class also supports other codes for country (region), such as 3-letter numeric UN M.49 area codes. Therefore, the list returned by this method does not contain ALL valid codes that can be used to obtain Locales.

    Note that this method does not return obsolete 2-letter country codes. ISO3166-3 codes which designate country codes for those obsolete codes, can be retrieved from `getISOCountries(Locale.IsoCountryCode type)` with `type` `Locale.IsoCountryCode.PART3`.

    Returns:
      An array of ISO 3166 two-letter country codes.

  - ### getISOCountries

    public static Set<String> getISOCountries(Locale.IsoCountryCode type)
    Returns an unmodifiable `Set` of ISO3166 country codes for the specified type.
    Parameters:
      `type` - `Locale.IsoCountryCode` specified ISO code type.
    Returns:
      an unmodifiable `Set` of ISO3166 country codes for the specified type
    Throws:
      `NullPointerException` - if type is null
    Since:
      9
    See Also:
      - `Locale.IsoCountryCode`

  - ### getISOLanguages

    public static String[] getISOLanguages()
    Returns a list of all 2-letter language codes defined in ISO 639. Can be used to obtain Locales.

    Note:

    - ISO 639 is not a stable standard— some languages' codes have changed. The list this function returns includes both the new and the old codes for the languages whose codes have changed.
    - The `Locale` class also supports language codes up to 8 characters in length. Therefore, the list returned by this method does not contain ALL valid codes that can be used to obtain Locales.
    Returns:
      An array of ISO 639 two-letter language codes.

  - ### getLanguage

    public String getLanguage()
    Returns the language code of this Locale.
    Implementation Note:
      This method returns the new forms for the obsolete ISO 639 codes ("iw", "ji", and "in"). See Legacy language codes for more information.
    Returns:
      The language code, or the empty string if none is defined.
    See Also:
      - `getDisplayLanguage()`

  - ### getScript

    public String getScript()
    Returns the script for this locale, which should either be the empty string or an ISO 15924 4-letter script code. The first letter is uppercase and the rest are lowercase, for example, 'Latn', 'Cyrl'.
    Returns:
      The script code, or the empty string if none is defined.
    Since:
      1.7
    See Also:
      - `getDisplayScript()`

  - ### getCountry

    public String getCountry()
    Returns the country/region code for this locale, which should either be the empty string, an uppercase ISO 3166 2-letter code, or a UN M.49 3-digit code.
    Returns:
      The country/region code, or the empty string if none is defined.
    See Also:
      - `getDisplayCountry()`

  - ### getVariant

    public String getVariant()
    Returns the variant code for this locale.
    Returns:
      The variant code, or the empty string if none is defined.
    See Also:
      - `getDisplayVariant()`

  - ### hasExtensions

    public boolean hasExtensions()
    Returns `true` if this `Locale` has any extensions.
    Returns:
      `true` if this `Locale` has any extensions
    Since:
      1.8

  - ### stripExtensions

    public Locale stripExtensions()
    Returns a copy of this `Locale` with no extensions. If this `Locale` has no extensions, this `Locale` is returned.
    Returns:
      a copy of this `Locale` with no extensions, or `this` if `this` has no extensions
    Since:
      1.8

  - ### getExtension

    public String getExtension(char key)
    Returns the extension (or private use) value associated with the specified key, or null if there is no extension associated with the key. To be well-formed, the key must be one of `[0-9A-Za-z]`. Keys are case-insensitive, so for example 'z' and 'Z' represent the same extension.
    Parameters:
      `key` - the extension key
    Returns:
      The extension, or null if this locale defines no extension for the specified key.
    Throws:
      `IllegalArgumentException` - if key is not well-formed
    Since:
      1.7
    See Also:
      - `PRIVATE_USE_EXTENSION`
      - `UNICODE_LOCALE_EXTENSION`

  - ### getExtensionKeys

    public Set<Character> getExtensionKeys()
    Returns the set of extension keys associated with this locale, or the empty set if it has no extensions. The returned set is unmodifiable. The keys will all be lower-case.
    Returns:
      The set of extension keys, or the empty set if this locale has no extensions.
    Since:
      1.7

  - ### getUnicodeLocaleAttributes

    public Set<String> getUnicodeLocaleAttributes()
    Returns the set of unicode locale attributes associated with this locale, or the empty set if it has no attributes. The returned set is unmodifiable.
    Returns:
      The set of attributes.
    Since:
      1.7

  - ### getUnicodeLocaleType

    public String getUnicodeLocaleType(String key)
    Returns the Unicode locale type associated with the specified Unicode locale key for this locale. Returns the empty string for keys that are defined with no type. Returns null if the key is not defined. Keys are case-insensitive. The key must be two alphanumeric characters ([0-9a-zA-Z]), or an IllegalArgumentException is thrown.
    Parameters:
      `key` - the Unicode locale key
    Returns:
      The Unicode locale type associated with the key, or null if the locale does not define the key.
    Throws:
      `IllegalArgumentException` - if the key is not well-formed
      `NullPointerException` - if `key` is null
    Since:
      1.7

  - ### getUnicodeLocaleKeys

    public Set<String> getUnicodeLocaleKeys()
    Returns the set of Unicode locale keys defined by this locale, or the empty set if this locale has none. The returned set is immutable. Keys are all lower case.
    Returns:
      The set of Unicode locale keys, or the empty set if this locale has no Unicode locale keywords.
    Since:
      1.7

  - ### toString

    public final String toString()
    Returns a string representation of this `Locale` object, consisting of language, country, variant, script, and extensions as below:

    > language + "_" + country + "_" + (variant + "_#" | "#") + script + "_" + extensions

    Language is always lower case, country is always upper case, script is always title case, and extensions are always lower case. Extensions and private use subtags will be in canonical order as explained in `toLanguageTag()`.

    When the locale has neither script nor extensions, the result is the same as in Java 6 and prior.

    If both the language and country fields are missing, this function will return the empty string, even if the variant, script, or extensions field is present (a locale with just a variant is not allowed, the variant must accompany a well-formed language or country code).

    If script or extensions are present and variant is missing, no underscore is added before the "#".

    This behavior is designed to support debugging and to be compatible with previous uses of `toString` that expected language, country, and variant fields only. To represent a Locale as a String for interchange purposes, use `toLanguageTag()`.

    Examples:

    - `en`
    - `de_DE`
    - `_GB`
    - `en_US_WIN`
    - `de__POSIX`
    - `zh_CN_#Hans`
    - `zh_TW_#Hant_x-java`
    - `th_TH_TH_#u-nu-thai`
    Overrides:
      `toString` in class `Object`
    Returns:
      A string representation of the Locale, for debugging.
    See Also:
      - `getDisplayName()`
      - `toLanguageTag()`

  - ### toLanguageTag

    public String toLanguageTag()
    Returns a well-formed IETF BCP 47 language tag representing this locale.

    If this `Locale` has a language, country, or variant that does not satisfy the IETF BCP 47 language tag syntax requirements, this method handles these fields as described below:

    Language: If language is empty, or not well-formed (for example "a" or "e2"), it will be emitted as "und" (Undetermined).

    Country: If country is not well-formed (for example "12" or "USA"), it will be omitted.

    Variant: If variant is well-formed, each sub-segment (delimited by '-' or '_') is emitted as a subtag. Otherwise:

    - if all sub-segments match `[0-9a-zA-Z]{1,8}` (for example "WIN" or "Oracle_JDK_Standard_Edition"), the first ill-formed sub-segment and all following will be appended to the private use subtag. The first appended subtag will be "lvariant", followed by the sub-segments in order, separated by hyphen. For example, "x-lvariant-WIN", "Oracle-x-lvariant-JDK-Standard-Edition".
    - if any sub-segment does not match `[0-9a-zA-Z]{1,8}`, the variant will be truncated and the problematic sub-segment and all following sub-segments will be omitted. If the remainder is non-empty, it will be emitted as a private use subtag as above (even if the remainder turns out to be well-formed). For example, "Solaris_isjustthecoolestthing" is emitted as "x-lvariant-Solaris", not as "solaris".

    Special Conversions: Java supports some old locale representations, including deprecated ISO language codes, for compatibility. This method performs the following conversions:

    - Deprecated ISO language codes "iw", "ji", and "in" are converted to "he", "yi", and "id", respectively.
    - A locale with language "no", country "NO", and variant "NY", representing Norwegian Nynorsk (Norway), is converted to a language tag "nn-NO".

    Note: Although the language tag obtained by this method is well-formed (satisfies the syntax requirements defined by the IETF BCP 47 specification), it is not necessarily a valid BCP 47 language tag. For example,

          Locale.forLanguageTag("xx-YY").toLanguageTag();

    will return "xx-YY", but the language subtag "xx" and the region subtag "YY" are invalid because they are not registered in the IANA Language Subtag Registry.
    Returns:
      a BCP47 language tag representing the locale
    Since:
      1.7
    See Also:
      - `forLanguageTag(String)`

  - ### caseFoldLanguageTag

    public static String caseFoldLanguageTag(String languageTag)
    Returns a case folded IETF BCP 47 language tag.

    This method formats a language tag into one with case convention that adheres to section 2.1.1. Formatting of Language Tags of RFC 5646. This format is defined as: All subtags, including extension and private use subtags, use lowercase letters with two exceptions: two-letter and four-letter subtags that neither appear at the start of the tag nor occur after singletons. Such two-letter subtags are all uppercase (as in the tags "en-CA-x-ca" or "sgn-BE-FR") and four- letter subtags are titlecase (as in the tag "az-Latn-x-latn"). As legacy tags, (defined as "grandfathered" in RFC 5646) are not always well-formed, this method will simply case fold a legacy tag to match the exact case convention for the particular tag specified in the respective `Legacy tags` table.

    Special Exceptions

    To maintain consistency with `variant` which is case-sensitive, this method will neither case fold variant subtags nor case fold private use subtags prefixed by `lvariant`.

    For example,

        String tag = "ja-kana-jp-x-lvariant-Oracle-JDK-Standard-Edition";
        Locale.caseFoldLanguageTag(tag); // returns "ja-Kana-JP-x-lvariant-Oracle-JDK-Standard-Edition"
        String tag2 = "ja-kana-jp-x-Oracle-JDK-Standard-Edition";
        Locale.caseFoldLanguageTag(tag2); // returns "ja-Kana-JP-x-oracle-jdk-standard-edition"

    Excluding case folding, this method makes no modifications to the tag itself. Case convention of language tags does not carry meaning, and is simply recommended as it corresponds with various ISO standards, including: ISO639-1, ISO15924, and ISO3166-1.

    As the formatting of the case convention is dependent on the positioning of certain subtags, callers of this method should ensure that the language tag is well-formed, (conforming to section 2.1. Syntax of RFC 5646).

    Parameters:
      `languageTag` - the IETF BCP 47 language tag.
    Returns:
      a case folded IETF BCP 47 language tag
    Throws:
      `IllformedLocaleException` - if `languageTag` is not well-formed
      `NullPointerException` - if `languageTag` is `null`
    Since:
      21
    External Specifications
      - RFC 5646: 2.1. Syntax
      - RFC 5646: 2.1.1. Formatting of Language Tags

  - ### forLanguageTag

    public static Locale forLanguageTag(String languageTag)
    Returns a locale for the specified IETF BCP 47 language tag string.

    If the specified language tag contains any ill-formed subtags, the first such subtag and all following subtags are ignored. Compare to `Locale.Builder.setLanguageTag(String)` which throws an exception in this case.

    Duplicate variants are accepted and included by the builder. However, duplicate extension singleton keys and their associated type are accepted but ignored. The same behavior applies to duplicate locale keys and attributes within a U extension. Note that subsequent subtags after the occurrence of a duplicate are not ignored.

    The following conversions are performed:

    - The language code "und" is mapped to language "".
    - The language codes "iw", "ji", and "in" are mapped to "he", "yi", and "id" respectively. (This is the same canonicalization that's done in Locale's constructors.) See Legacy language codes for more information.
    - The portion of a private use subtag prefixed by "lvariant", if any, is removed and appended to the variant field in the result locale (without case normalization). If it is then empty, the private use subtag is discarded:

              Locale loc;
              loc = Locale.forLanguageTag("en-US-x-lvariant-POSIX");
              loc.getVariant(); // returns "POSIX"
              loc.getExtension('x'); // returns null

              loc = Locale.forLanguageTag("de-POSIX-x-URP-lvariant-Abc-Def");
              loc.getVariant(); // returns "POSIX_Abc_Def"
              loc.getExtension('x'); // returns "urp"

    - BCP 47 language tags permit up to three extlang subtags. However, the second and third extlang subtags are always ignored. As such, the first extlang subtag in `languageTag` is used as the language, and the primary language subtag and other extlang subtags are ignored. Language tags that exceed three extlang subtags are considered ill-formed starting at the offending extlang subtag.

              Locale.forLanguageTag("ar-aao").getLanguage(); // returns "aao"
              Locale.forLanguageTag("en-abc-def-us").toString(); // returns "abc_US"
              Locale.forLanguageTag("zh-yue-gan-cmn-czh-CN").toString();
              // returns "yue"; "czh" exceeds the extlang limit, and subsequent
              // subtags are considered ill-formed

    - Case is normalized except for variant tags, which are left unchanged. Language is normalized to lower case, script to title case, country to upper case, and extensions to lower case.
    - If, after processing, the locale would exactly match either ja_JP_JP or th_TH_TH with no extensions, the appropriate extensions are added as though the constructor had been called:

             Locale.forLanguageTag("ja-JP-x-lvariant-JP").toLanguageTag();
             // returns "ja-JP-u-ca-japanese-x-lvariant-JP"
             Locale.forLanguageTag("th-TH-x-lvariant-TH").toLanguageTag();
             // returns "th-TH-u-nu-thai-x-lvariant-TH"

    This implements the 'Language-Tag' production of BCP47, and so supports legacy (regular and irregular, referred to as "Type: grandfathered" in BCP47) as well as private use language tags. Stand alone private use tags are represented as empty language and extension 'x-whatever', and legacy tags are converted to their canonical replacements where they exist.

    Legacy tags with canonical replacements are as follows:

    Legacy tags with canonical replacements
    legacy tag | modern replacement
    --- | ---
    art-lojban | jbo
    i-ami | ami
    i-bnn | bnn
    i-hak | hak
    i-klingon | tlh
    i-lux | lb
    i-navajo | nv
    i-pwn | pwn
    i-tao | tao
    i-tay | tay
    i-tsu | tsu
    no-bok | nb
    no-nyn | nn
    sgn-BE-FR | sfb
    sgn-BE-NL | vgt
    sgn-CH-DE | sgg
    zh-guoyu | cmn
    zh-hakka | hak
    zh-min-nan | nan
    zh-xiang | hsn

    Legacy tags with no modern replacement will be converted as follows:

    Legacy tags with no modern replacement
    legacy tag | converts to
    --- | ---
    cel-gaulish | xtg-x-cel-gaulish
    en-GB-oed | en-GB-x-oed
    i-default | en-x-i-default
    i-enochian | und-x-i-enochian
    i-mingo | see-x-i-mingo
    zh-min | nan-x-zh-min

    For a list of all legacy tags, see the IANA Language Subtag Registry (search for "Type: grandfathered").

    Note: there is no guarantee that `toLanguageTag` and `forLanguageTag` will round-trip.

    Parameters:
      `languageTag` - the language tag
    Returns:
      The locale that best represents the language tag.
    Throws:
      `NullPointerException` - if `languageTag` is `null`
    Since:
      1.7
    See Also:
      - `toLanguageTag()`
      - `Locale.Builder.setLanguageTag(String)`

  - ### getISO3Language

    public String getISO3Language() throws MissingResourceException
    Returns a three-letter abbreviation of this locale's language. If the language matches an ISO 639-1 two-letter code, the corresponding ISO 639-2/T three-letter lowercase code is returned. The ISO 639-2 language codes can be found on-line, see "Codes for the Representation of Names of Languages Part 2: Alpha-3 Code". If the locale specifies a three-letter language, the language is returned as is. If the locale does not specify a language the empty string is returned.
    Returns:
      a three-letter abbreviation of this locale's language
    Throws:
      `MissingResourceException` - Throws MissingResourceException if three-letter language abbreviation is not available for this locale.

  - ### getISO3Country

    public String getISO3Country() throws MissingResourceException
    Returns a three-letter abbreviation of this locale's country. If the country matches an ISO 3166-1 alpha-2 code, the corresponding ISO 3166-1 alpha-3 uppercase code is returned. If the locale doesn't specify a country, this will be the empty string.

    The ISO 3166-1 codes can be found on-line.

    Returns:
      a three-letter abbreviation of this locale's country
    Throws:
      `MissingResourceException` - Throws MissingResourceException if the three-letter country abbreviation is not available for this locale.

  - ### getDisplayLanguage

    public final String getDisplayLanguage()
    Returns a name for the locale's language that is appropriate for display to the user. If possible, the name returned will be localized for the default `DISPLAY` locale. For example, if the locale is fr_FR and the default `DISPLAY` locale is en_US, getDisplayLanguage() will return "French"; if the locale is en_US and the default `DISPLAY` locale is fr_FR, getDisplayLanguage() will return "anglais". If the name returned cannot be localized for the default `DISPLAY` locale, this function falls back on the English name, and uses the ISO code as a last-resort value. If the locale doesn't specify a language, this function returns the empty string.
    Returns:
      The name of the display language.

  - ### getDisplayLanguage

    public String getDisplayLanguage(Locale inLocale)
    Returns a name for the locale's language that is appropriate for display to the user. If possible, the name returned will be localized according to inLocale. For example, if the locale is fr_FR and inLocale is en_US, getDisplayLanguage() will return "French"; if the locale is en_US and inLocale is fr_FR, getDisplayLanguage() will return "anglais". If the name returned cannot be localized according to inLocale, this function falls back on the English name, and finally on the ISO code as a last-resort value. If the locale doesn't specify a language, this function returns the empty string.
    Parameters:
      `inLocale` - The locale for which to retrieve the display language.
    Returns:
      The name of the display language appropriate to the given locale.
    Throws:
      `NullPointerException` - if `inLocale` is `null`

  - ### getDisplayScript

    public String getDisplayScript()
    Returns a name for the locale's script that is appropriate for display to the user. If possible, the name will be localized for the default `DISPLAY` locale. Returns the empty string if this locale doesn't specify a script code.
    Returns:
      the display name of the script code for the current default `DISPLAY` locale
    Since:
      1.7

  - ### getDisplayScript

    public String getDisplayScript(Locale inLocale)
    Returns a name for the locale's script that is appropriate for display to the user. If possible, the name will be localized for the given locale. Returns the empty string if this locale doesn't specify a script code.
    Parameters:
      `inLocale` - The locale for which to retrieve the display script.
    Returns:
      the display name of the script code for the current default `DISPLAY` locale
    Throws:
      `NullPointerException` - if `inLocale` is `null`
    Since:
      1.7

  - ### getDisplayCountry

    public final String getDisplayCountry()
    Returns a name for the locale's country that is appropriate for display to the user. If possible, the name returned will be localized for the default `DISPLAY` locale. For example, if the locale is fr_FR and the default `DISPLAY` locale is en_US, getDisplayCountry() will return "France"; if the locale is en_US and the default `DISPLAY` locale is fr_FR, getDisplayCountry() will return "Etats-Unis". If the name returned cannot be localized for the default `DISPLAY` locale, this function falls back on the English name, and uses the ISO code as a last-resort value. If the locale doesn't specify a country, this function returns the empty string.
    Returns:
      The name of the country appropriate to the locale.

  - ### getDisplayCountry

    public String getDisplayCountry(Locale inLocale)
    Returns a name for the locale's country that is appropriate for display to the user. If possible, the name returned will be localized according to inLocale. For example, if the locale is fr_FR and inLocale is en_US, getDisplayCountry() will return "France"; if the locale is en_US and inLocale is fr_FR, getDisplayCountry() will return "Etats-Unis". If the name returned cannot be localized according to inLocale, this function falls back on the English name, and finally on the ISO code as a last-resort value. If the locale doesn't specify a country, this function returns the empty string.
    Parameters:
      `inLocale` - The locale for which to retrieve the display country.
    Returns:
      The name of the country appropriate to the given locale.
    Throws:
      `NullPointerException` - if `inLocale` is `null`

  - ### getDisplayVariant

    public final String getDisplayVariant()
    Returns a name for the locale's variant code that is appropriate for display to the user. If possible, the name will be localized for the default `DISPLAY` locale. If the locale doesn't specify a variant code, this function returns the empty string.
    Returns:
      The name of the display variant code appropriate to the locale.

  - ### getDisplayVariant

    public String getDisplayVariant(Locale inLocale)
    Returns a name for the locale's variant code that is appropriate for display to the user. If possible, the name will be localized for inLocale. If the locale doesn't specify a variant code, this function returns the empty string.
    Parameters:
      `inLocale` - The locale for which to retrieve the display variant code.
    Returns:
      The name of the display variant code appropriate to the given locale.
    Throws:
      `NullPointerException` - if `inLocale` is `null`

  - ### getDisplayName

    public final String getDisplayName()
    Returns a name for the locale that is appropriate for display to the user. This will be the values returned by getDisplayLanguage(), getDisplayScript(), getDisplayCountry(), getDisplayVariant() and optional Unicode extensions assembled into a single string. The non-empty values are used in order, with the second and subsequent names in parentheses. For example:

    > language (script, country, variant(, extension)*)
    > language (country(, extension)*)
    > language (variant(, extension)*)
    > script (country(, extension)*)
    > country (extension)*

    depending on which fields are specified in the locale. The field separator in the above parentheses, denoted as a comma character, may be localized depending on the locale. If the language, script, country, and variant fields are all empty, this function returns the empty string.
    Returns:
      The name of the locale appropriate to display.

  - ### getDisplayName

    public String getDisplayName(Locale inLocale)
    Returns a name for the locale that is appropriate for display to the user. This will be the values returned by getDisplayLanguage(), getDisplayScript(), getDisplayCountry(), getDisplayVariant(), and optional Unicode extensions assembled into a single string. The non-empty values are used in order, with the second and subsequent names in parentheses. For example:

    > language (script, country, variant(, extension)*)
    > language (country(, extension)*)
    > language (variant(, extension)*)
    > script (country(, extension)*)
    > country (extension)*

    depending on which fields are specified in the locale. The field separator in the above parentheses, denoted as a comma character, may be localized depending on the locale. If the language, script, country, and variant fields are all empty, this function returns the empty string.
    Parameters:
      `inLocale` - The locale for which to retrieve the display name.
    Returns:
      The name of the locale appropriate to display.
    Throws:
      `NullPointerException` - if `inLocale` is `null`

  - ### clone

    public Object clone()
    Overrides Cloneable.
    Overrides:
      `clone` in class `Object`
    Returns:
      a clone of this instance.
    See Also:
      - `Cloneable`

  - ### hashCode

    public int hashCode()
    Override hashCode. Since Locales are often used in hashtables, caches the value for speed.
    Overrides:
      `hashCode` in class `Object`
    Returns:
      a hash code value for this object
    See Also:
      - `Object.equals(java.lang.Object)`
      - `System.identityHashCode(Object)`

  - ### equals

    public boolean equals(Object obj)
    Returns true if this Locale is equal to another object. A Locale is deemed equal to another Locale with identical language, script, country, variant and extensions, and unequal to all other objects.
    Overrides:
      `equals` in class `Object`
    Parameters:
      `obj` - the reference object with which to compare.
    Returns:
      true if this Locale is equal to the specified object.
    See Also:
      - `Object.hashCode()`
      - `HashMap`

  - ### filter

    public static List<Locale> filter(List<Locale.LanguageRange> priorityList, Collection<Locale> locales, Locale.FilteringMode mode)
    Returns a list of matching `Locale` instances using the filtering mechanism defined in RFC 4647. This filter operation on the given `locales` ensures that only unique matching locale(s) are returned.
    Parameters:
      `priorityList` - user's Language Priority List in which each language tag is sorted in descending order based on priority or weight
      `locales` - `Locale` instances used for matching
      `mode` - filtering mode
    Returns:
      a list of `Locale` instances for matching language tags sorted in descending order based on priority or weight, or an empty list if nothing matches. The list is modifiable.
    Throws:
      `NullPointerException` - if `priorityList` or `locales` is `null`
      `IllegalArgumentException` - if one or more extended language ranges are included in the given list when `Locale.FilteringMode.REJECT_EXTENDED_RANGES` is specified
    Since:
      1.8

  - ### filter

    public static List<Locale> filter(List<Locale.LanguageRange> priorityList, Collection<Locale> locales)
    Returns a list of matching `Locale` instances using the filtering mechanism defined in RFC 4647. This is equivalent to `filter(List, Collection, FilteringMode)` when `mode` is `Locale.FilteringMode.AUTOSELECT_FILTERING`. This filter operation on the given `locales` ensures that only unique matching locale(s) are returned.
    Parameters:
      `priorityList` - user's Language Priority List in which each language tag is sorted in descending order based on priority or weight
      `locales` - `Locale` instances used for matching
    Returns:
      a list of `Locale` instances for matching language tags sorted in descending order based on priority or weight, or an empty list if nothing matches. The list is modifiable.
    Throws:
      `NullPointerException` - if `priorityList` or `locales` is `null`
    Since:
      1.8

  - ### filterTags

    public static List<String> filterTags(List<Locale.LanguageRange> priorityList, Collection<String> tags, Locale.FilteringMode mode)
    Returns a list of matching languages tags using the basic filtering mechanism defined in RFC 4647. This filter operation on the given `tags` ensures that only unique matching tag(s) are returned with preserved case. In case of duplicate matching tags with the case difference, the first matching tag with preserved case is returned. For example, "de-ch" is returned out of the duplicate matching tags "de-ch" and "de-CH", if "de-ch" is checked first for matching in the given `tags`. Note that if the given `tags` is an unordered `Collection`, the returned matching tag out of duplicate tags is subject to change, depending on the implementation of the `Collection`.
    Parameters:
      `priorityList` - user's Language Priority List in which each language tag is sorted in descending order based on priority or weight
      `tags` - language tags
      `mode` - filtering mode
    Returns:
      a list of matching language tags sorted in descending order based on priority or weight, or an empty list if nothing matches. The list is modifiable.
    Throws:
      `NullPointerException` - if `priorityList` or `tags` is `null`
      `IllegalArgumentException` - if one or more extended language ranges are included in the given list when `Locale.FilteringMode.REJECT_EXTENDED_RANGES` is specified
    Since:
      1.8

  - ### filterTags

    public static List<String> filterTags(List<Locale.LanguageRange> priorityList, Collection<String> tags)
    Returns a list of matching languages tags using the basic filtering mechanism defined in RFC 4647. This is equivalent to `filterTags(List, Collection, FilteringMode)` when `mode` is `Locale.FilteringMode.AUTOSELECT_FILTERING`. This filter operation on the given `tags` ensures that only unique matching tag(s) are returned with preserved case. In case of duplicate matching tags with the case difference, the first matching tag with preserved case is returned. For example, "de-ch" is returned out of the duplicate matching tags "de-ch" and "de-CH", if "de-ch" is checked first for matching in the given `tags`. Note that if the given `tags` is an unordered `Collection`, the returned matching tag out of duplicate tags is subject to change, depending on the implementation of the `Collection`.
    Parameters:
      `priorityList` - user's Language Priority List in which each language tag is sorted in descending order based on priority or weight
      `tags` - language tags
    Returns:
      a list of matching language tags sorted in descending order based on priority or weight, or an empty list if nothing matches. The list is modifiable.
    Throws:
      `NullPointerException` - if `priorityList` or `tags` is `null`
    Since:
      1.8

  - ### lookup

    public static Locale lookup(List<Locale.LanguageRange> priorityList, Collection<Locale> locales)
    Returns a `Locale` instance for the best-matching language tag using the lookup mechanism defined in RFC 4647.
    Parameters:
      `priorityList` - user's Language Priority List in which each language tag is sorted in descending order based on priority or weight
      `locales` - `Locale` instances used for matching
    Returns:
      the best matching `Locale` instance chosen based on priority or weight, or `null` if nothing matches.
    Throws:
      `NullPointerException` - if `priorityList` or `locales` is `null`
    Since:
      1.8

  - ### lookupTag

    public static String lookupTag(List<Locale.LanguageRange> priorityList, Collection<String> tags)
    Returns the best-matching language tag using the lookup mechanism defined in RFC 4647. This lookup operation on the given `tags` ensures that the first matching tag with preserved case is returned.
    Parameters:
      `priorityList` - user's Language Priority List in which each language tag is sorted in descending order based on priority or weight
      `tags` - language tags used for matching
    Returns:
      the best matching language tag chosen based on priority or weight, or `null` if nothing matches.
    Throws:
      `NullPointerException` - if `priorityList` or `tags` is `null`
    Since:
      1.8