Here's a language tree I whipped up in Paint for a future campaign setting I've been working on (click to enlarge):
Professor Tolkien I'm not, but I've always been interesting in languages in an RPG. Why is there a "Common" tongue? Where does it come from? I created this chart to help flesh out my own answers, and hopefully for player entertainment as well.
I plan to do one for the Trollish, Orcish, and Ogrish tongues soon.