Spellcheck is one major feature that I know FireFox has built in, I'm not sure about IE though... IMO it's a waste of resources, as it'd have to be maintained, and not all UBB customers are US Citizens, so multiple dictionaries would require upkeep...
IE does not have a spellchecker build into it. I'm sure there are more people using IE then FF so it might just be a good use of resources.
I do agree other languages would be needed, that is for sure. I wonder if there are freeware language packs out there that might make this task easier?