Celebrim
Legend
Then again, I know 2 languages pretty well- English as a native speaker and German as a 3 year resident (with subsequent returns)- plus a smattering of a few others.
Great.
But there are over 5000 languages in the world, and in historical times the number probably climbed over 10,000. The existance of very wide spread langauges like English is a relatively modern phenomenom. Even more modern is the reduction in the range of ways in which a language is spoken, so that as a result of mass media, someone from Boston and someone from rural Alabama have a lot easier time understanding each other now than even 100 years ago.
Generally speaking there are in the real world more language families (like Latin, Germanic, Dravidic or what have you) than the number of languages normally spoken in RPGs.
'Common' proves to be a very reasonable simplificiation since not being able to communicate isn't particularly conducive to role-playing.