locales

Locales are a collection of cultural rules and settings that define how information is presented to users in a given region. They specify language, regional conventions, and often a text encoding, guiding software to adapt interfaces, data formatting, and input handling to local expectations. A locale affects language for user interfaces, date and time formats, numeric and monetary formats, measurement units, collation (sorting), and even text direction.

In computing, a locale is identified by a code or tag composed from language, territory, and possibly script and variant. Common forms include en_US, fr_FR, and zh_CN. A running system may also specify an encoding, as in en_US.UTF-8. In modern practice, IETF BCP 47 language tags (for example, fr-CA, zh-Hant-CN) are widely used, often with a separate region and script. Locale data comes from standardized repositories such as the Unicode CLDR and, for historical reasons, POSIX locale data.

Locales primarily influence formatting and sorting: numbers use local decimal separators and digit grouping, dates and times follow regional formats, currencies use local symbols and placement, and collation rules determine order in lists. Pluralization rules and measurement systems can also vary by locale.

Software uses locales through libraries and environment variables, such as LANG and LC_ALL, and through APIs in languages like Java, Python, .NET, and C/C++. Applications may switch locales at runtime to present translated text and region-specific formatting. Challenges include incomplete coverage, evolving standards, and the complexity of plural and script rules across locales.