Named Locales
In the Internationalization Module, a locale name consists of one or more of the following components, in the following order:
a two-letter, lowercase ISO-639 language code
an optional two-letter, uppercase ISO-3166 country code
an optional variant code representing variations within a language-country pair; the variant name may be compound, composed of two or more variants joined by an underbar
Multiple components are joined by underbars. For example, locale zh_TW contains the ISO-639 language code for Chinese and the ISO-3166 country code for Taiwan. Locale es_ES_TRADITIONAL uses a variant code to specify traditional Spanish.