What do you mean? Input? Display? Translations?
Input: ... I dunno, I dont think anybody thought of russian when designing the pandora keyboard....
Display: I think if you set LANG to something supporting UTF-8 it can display lots of stuff.
Translations: Nothing shipped by default in the linux - my guess is because NAND space is really tight as it is.
LANG is not set by default, so its ISO8859-1 + "C" locale by stock. glibc localedata (and "locale-base-*") is installed for de-de,en-gb,en-us,es-es and fr-fr.
As for adding more, there seems to be "angstrom-locale-*-feed-config" packages for lots of languages (my guess is that they provide translations for various packages in their language).
So, if you want it to be entirely in another language, my guess is that you will need to get geeky to do that, but it's not impossible. Boot from SD, set "LANG", install lots of packages and I think it might work...