Well, assume you download a demo of a game you are anticipating, and then realize it's say in Czech, and you don't understand a word. Wouldn't you be disappointed?
I doubt you can learn a language from a computer game, you can certainly improve it (like I did with English), but not if you don't understand anything. I'd say, let the people know it's the German demo, and let them decide. <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" />
