Originally Posted by DjNDB
If you have a German windows, that's caused by a missing registry key. I have posted reg files to fix it here
It depends on your Windows Version though. If you have Vista, you can give the Win7 Reg file a try. No harm in trying, since you can just remove it again with the appropriate removal file.
Thank you so much, this immediately fixed the problem.
I was already afraid that I would have to always change the system locale before playing (I have an English Windows, the game seems to use the locale unless the registry key is there).