Moderators do a difficult job and should be thanked for what they do.
People have to be warned occasionally - or even in the extreme - have membership of forum revoked as deemed fit.
The only issue I see with this thread is - the person does not know why they have been the recipient of the ultimate sanction. If a sanction is imposed, it should always come with an explanation in the hope that the the person will learn from it, or have a chance to challenge it.
I could be wrong, but how many of us here speak fluent German?
I'm English, not American, Canadian or from similar international English speaking country - and I find various comments from people of those countries to be 'challenging to accept' - but often put it down to getting 'lost in translation'.
When some one from a non English speaking country engages in an English speaking forum, I'm often inclined to be impressed that they have such language skills and feel embarrassed at my failure to reciprocate - but also I'm inclined to give them a bit more latitude than I would for a person raised up with English as a first language. And of all the languages - there is a reason German is not amongst the top spoken languages in the world - it does not translate well, as my wife who spent 20 years living in Gemany will attest.
Ban the guy by all means, but at least tell him why and see if he has erred in his usage of the English language!