Not a lot of people know it, but both Windows and Office are available in up to 70 languages (probably more when you read this, they release on a rolling basis).
The "LIP" (Language Interface Pack) is a translated skin that sits on top of a licensed copy of Office or Windows. When you've installed the LIP pack, you can switch the interface between the base langauge (for example English) and your local langauge. So, you can have and English Office base version, with a Welsh "LIP" on top - or a Spanish base version with Catalan on top.
For Office, get more info on the Office Language Interface Pack blog.
Rob Margel - Windows International Site Manager UK - seems to keep track of new Windows Vista LIP releases on his blog. The last one was Armenian in October so it's well worth keeping an eye on his blog if you are interested in LIPs.
For Office, the LIP usually includes a speller for the language as well.