maybe you should make a language rule. I find it a little bit irritating to see english and german topics mixed up in one Board.
Maybe part/mirror the categories as "German area" and "english area" with same boards but where one the corresponding language is allowed.
Or you maybe should say "english only please" and only make a small "Support in German" Area for that people that couldn't write / read english good enough to communicate the problems they have.
Also, maybe it would be a good idea to make a "don't make jokes about other people's english"