to
Builds a locale identifier (e.g. en_US) from an ISO 639-1 language code and this country's ISO 3166-1 alpha-2 code.
Return
The locale string in language_REGION format.
Parameters
language6391
ISO 639-1 two-letter language code (e.g. "en").
Throws
Illegal
if language6391 is not exactly 2 characters long.