The Apple TV, a device which lets you put digital content from Macs and PCs running iTunes onto your TV screen, uses a customized version of OS X which apparently has somewhat different language capabilities than the full one. Although not mentioned in Apple's specs for the product, you can choose the language for menus and dialogues in Settings > Language, where the choices are English, Danish, Spanish, Korean, Japanese, Traditional and Simplified Chinese, Finnish, French, Dutch, Russian, German, Italian, Norwegian, and Swedish. This adds Russian and subtracts Portuguese from the OS X 10.4 list.
Regarding display, this note gives a somewhat odd list of languages *not* supported, presumably because the fonts are not provided, but surely there are more, including Vietnamese, Tamil, and Devanagari and other Indic scripts. Hopefully this list will be reduced via software updates in the future.
Reports indicate that input, for example in search fields, probably does not support languages other than English.