Voice acting (French. English, German and Russian possible)
Sound/music editing
Mods translation (from/to French, English, German, and just a little bit from Russian)
Mod stories writing
It depends. At least in Radiant 1.5, if you go beyond +32000 or -32000 units in any direction those brushes and entities will be deleted. Other times it can happen due to simply strangely shaped brushes that the program doesn't seem to like.