Of course, insults should not be written, no matter which language.
English is not my first language and I can not bring over something as well as I could in my mother language. So I feel tempted, to write a comment in German, to a German member here. Simply because in German, it works better.
I understand the other comments too, people want to understand what the hell is written there, in a foreign language.
What about the idea, to - IF someone "must" (does feel, it has to be) write a German in own native language - the person must provide an English translation underneath the comment, so that everyone can understand it. I would VERY MUCH favour this, and it would give credit for both parties here.
Greetings,
Cornelia