1 // Copyright 2017 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
5 // Package language implements BCP 47 language tags and related functionality.
7 // The most important function of package language is to match a list of
8 // user-preferred languages to a list of supported languages.
9 // It alleviates the developer of dealing with the complexity of this process
10 // and provides the user with the best experience
11 // (see https://blog.golang.org/matchlang).
14 // Matching preferred against supported languages
16 // A Matcher for an application that supports English, Australian English,
17 // Danish, and standard Mandarin can be created as follows:
19 // var matcher = language.NewMatcher([]language.Tag{
20 // language.English, // The first language is used as fallback.
21 // language.MustParse("en-AU"),
26 // This list of supported languages is typically implied by the languages for
27 // which there exists translations of the user interface.
29 // User-preferred languages usually come as a comma-separated list of BCP 47
31 // The MatchString finds best matches for such strings:
33 // handler(w http.ResponseWriter, r *http.Request) {
34 // lang, _ := r.Cookie("lang")
35 // accept := r.Header.Get("Accept-Language")
36 // tag, _ := language.MatchStrings(matcher, lang.String(), accept)
38 // // tag should now be used for the initialization of any
39 // // locale-specific service.
42 // The Matcher's Match method can be used to match Tags directly.
44 // Matchers are aware of the intricacies of equivalence between languages, such
45 // as deprecated subtags, legacy tags, macro languages, mutual
46 // intelligibility between scripts and languages, and transparently passing
47 // BCP 47 user configuration.
48 // For instance, it will know that a reader of Bokmål Danish can read Norwegian
49 // and will know that Cantonese ("yue") is a good match for "zh-HK".
52 // Using match results
54 // To guarantee a consistent user experience to the user it is important to
55 // use the same language tag for the selection of any locale-specific services.
56 // For example, it is utterly confusing to substitute spelled-out numbers
57 // or dates in one language in text of another language.
58 // More subtly confusing is using the wrong sorting order or casing
59 // algorithm for a certain language.
61 // All the packages in x/text that provide locale-specific services
62 // (e.g. collate, cases) should be initialized with the tag that was
63 // obtained at the start of an interaction with the user.
65 // Note that Tag that is returned by Match and MatchString may differ from any
66 // of the supported languages, as it may contain carried over settings from
68 // This may be inconvenient when your application has some additional
69 // locale-specific data for your supported languages.
70 // Match and MatchString both return the index of the matched supported tag
71 // to simplify associating such data with the matched tag.
76 // If one uses the Matcher to compare languages one does not need to
77 // worry about canonicalization.
79 // The meaning of a Tag varies per application. The language package
80 // therefore delays canonicalization and preserves information as much
81 // as possible. The Matcher, however, will always take into account that
82 // two different tags may represent the same language.
84 // By default, only legacy and deprecated tags are converted into their
85 // canonical equivalent. All other information is preserved. This approach makes
86 // the confidence scores more accurate and allows matchers to distinguish
87 // between variants that are otherwise lost.
89 // As a consequence, two tags that should be treated as identical according to
90 // BCP 47 or CLDR, like "en-Latn" and "en", will be represented differently. The
91 // Matcher handles such distinctions, though, and is aware of the
92 // equivalence relations. The CanonType type can be used to alter the
93 // canonicalization form.
97 // BCP 47 - Tags for Identifying Languages http://tools.ietf.org/html/bcp47
99 package language // import "golang.org/x/text/language"
101 // TODO: explanation on how to match languages for your own locale-specific