freebsd-dev/share/mklocale
..
README.locale_name

Locale name string format must be compliant with XPG3 and
using following format.
	<locale name>   ::= <language>_<territory>.<encoding>
	<language>      ::= based on ISO 639
	<territory>     ::= based on ISO 3166 (country code)
	<encoding>      ::= "EUC", "KOI8-R", ...