Facebook uses a
xx_XX format for representing locales like:
jp_JP, etc. We're actively working on separating our
country combinations internally, and where we go from there as far as standards go is unknown. BUT if you'd like to help support
bcp-47 standards or similar, you are very welcome to contribute!
We generate all our number variation data found in our
IntlNumberTypes internals from CLDR (Unicode Common Locale Data Repository).