Honestly, I have no idea.
I don't remember the language system in 2.1.1 very well (and it is completely changed in trunk), so all I can say is:
1) if you have XYZ locale in your system, AND
2) if you have ufoai.mo for XYZ in base/i18n/, AND
3) you started the game with such locales (+set s_language XYZ)
it should work.
Maybe something is just broken for FreeBSD port. Maybe you could dig into it. Try to do some excercises. Set your LC_MESSAGES to en_GB.UTF-8. Copy base/i18n/en/ to base/i18n/en_GB/. Try to s_language "en_GB" if "en_GB.UTF-8" does not work.
Good luck.
