localeidentifiers

Locale identifiers are strings that designate language, script, country/region, and optional variants for software localization. They guide translation selection, number and date formatting, collation, and input methods.

The predominant standard for new systems is IETF BCP 47 language tags, which use subtags for language (e.g., en), script (e.g., Latn), region (e.g., US), variant, and extensions. Examples: en, en-US, en-Latn-US, zh-Hans-CN. Older POSIX and some operating systems use different forms like en_US.UTF-8, and Windows uses LCID or culture names such as en-US.

Structure: A typical locale identifier includes language, optional script, optional region, and optional variants or extensions. The tags are case-insensitive in practice; canonical form generally uses lower-case language, upper-case region, and hyphens as separators in BCP 47. Variants and extensions add further specificity, such as collation or calendar preferences.

Usage: Systems select resources (translations, date/time formats, number formats) based on the best-matching locale. CLDR provides data that underpins these formats; software may implement fallbacks if an exact match is not available.

Interoperability: Different platforms map or adapt locale identifiers differently; converting between BCP 47 tags and legacy forms can be necessary. Library support exists in ICU, Java, .NET, and many web frameworks.

See also: Locale, Internationalization, Localization, BCP 47, CLDR.