Summary

Define APIs so that applications that use BCP 47 language tags (seeRFC 5646) can match them to a user's language preferences in away that conforms toRFC 4647.

Motivation

It's a common scenario across applications, platforms, and/or protocols to needto specify a set of language tags (i.e., a range of languages), and match agiven language tag against such a set, e.g., a user's preferred set oflanguages. Java SE 8 will provide a full BCP 47 implementation according toRFC 5646.

Description

Implement the functionality defined inRFC 4647, whose descriptionis as follows:

This document describes a syntax, called a "language-range", for specifyingitems in a user's list of language preferences. It also describes differentmechanisms for comparing and matching these to language tags. Two kinds ofmatching mechanisms, filtering and lookup, are defined. Filtering produces a(potentially empty) set of language tags, whereas lookup produces a singlelanguage tag. Possible applications include language negotiation or contentselection.

The basic ideas of the API to be proposed are:

1. Implement the Language Range with aCollection<String>, and the LanguagePriority List with aList<String>.

2. Provide a few methods that implement the following:

   • Basic filtering: Take the Basic Language Range and the Language PriorityList, and returning the filtered set of Language Tags.
   • Extended filtering: Take the Extended Language Range and the LanguagePriority List, and return the filtered set of Language Tags.
   • Lookup: Take the Basic Language Range and the Language Priority List,and return the best matched Language Tag.

Example: Here's a person who speaks Japanese("ja") as mother tongue,English("en") and German("de") as the second languages. He lives in Japan.And, here's an application which happens to have localization resource data forEnglish, French, New Caledonian Javanese, and Japanese.

The above situation could be expressed like this with the new API:

/* Basic language ranges for this user's language priority list:  *   ja-JP: Japanese used in Japan *   en-jp: English used in Japan *   de-JP: German used in Japan * * The order expresses the priority of each language for the user. * Note that each sub tag (e.g. "jp") are case insensitive and used after * normalization. */List<String> list1 = Arrays.asList("ja-JP", "en-jp", "de-JP");/* Extended language ranges for this user's language priority list:  *   ja-*-JP: Japanese used in Japan *   en-*-jp: English used in Japan *   de-*-JP: German used in Japan * * The order expresses the priority of each language for the user. * Note that each sub tag (e.g. "jp") are case insensitive and used after * normalization. */List<String> list2 = Arrays.asList("ja-*-JP", "en-*-jp", "de-*-JP");/* The app's language ranges: *   en-US: English used in the USA *   en-JP: Japanese used in the USA *   fr-FR: French used in France, *   de-de: German used in Germany *   de-CH: German used in Switzerland *   de-jp: German used in Japan *   jas-JP: New Caledonian Javanese used in Japan *   ja-US: Japanese used in the USA */  ja-Latn-JP: Japanese used in Japan, written in Latin alphabetCollection<String> ranges =    Arrays.asList("en-US", "en-JP", "fr-FR", "de-DE", "de-CH", "de-JP",                  "ja-US", "jas-JP", "ja-Latn-JP");// Matching 1: Basic filtering returns a list of "en-JP" and// "de-JP".List<Locale> tags1 = Locale.filterBasic(list1, ranges);// Matching 2: Extended filtering returns a list of "ja-Latn-JP",// "en-JP", and "de-JP".List<Locale> tags2 = Locale.filterExtended(list2, ranges);// Matching 3: Look up returns "en-JP".Locale locale = Locale.lookup(list1, ranges);</code>

Note that the API introduced here is a draft and may be changed later.