A key concept for application programs is that of a program's locale. The locale is an explicit model and definition of a native-language environment. The notion of a locale is explicitly defined and included in the POSIX standard which can be accessed through http://opengroup.org.
A locale consists of a number of categories for which country-dependent formatting or other specifications exist. A program's locale defines its code sets, date and time formatting conventions, monetary conventions, decimal formatting conventions, and collation (sort) order.
A locale name can be composed of a base language, country (territory) of use, and codeset. For example, German language is de, an abbreviation for Deutsch, while Swiss German is de_CH, CH being an abbreviation for Confederation Helvetica. This convention allows for specific differences by country, such as currency unit notation. In Oracle Solaris 11 the default locale codeset is UTF-8, an ASCII compatible 8-bit encoding form of Unicode. The fully defined locale name for Swiss German would thus be de_CH.UTF-8.
More than one locale can be associated with a particular language, which allows for regional differences. For example, an English-speaking user in the United States can select the en_US.UTF-8 locale (English for the United States), while an English-speaking user in Great Britain can select en_GB.UTF-8 (English for Great Britain).
Generally the locale name is specified by the LANG environment variable. Locale categories are subordinate to LANG but can be set separately, in which case they override LANG. If the LC_ALL environment variable is set, it overrides LANG and all the separate locale categories.
The locale naming convention is:
language[_territory][.codeset][@modifier]
where a two-letter language code is from ISO 639, a two-letter territory code is from ISO 3166, codeset is the name of the codeset that is being used in the locale, and modifier is the name of the characteristics that differentiate the locale from the locale without the modifier.
All Oracle Solaris product locales preserve the Portable Character Set characters with US-ASCII code values.
For more information about the portable character set, refer to X/Open CAE Specification: System Interface Definitions, Issue 5" (ISBN 1-85912-186-1).
A single locale can have more than one locale name. For example, POSIX is the same locale as C.