Since the phone already is 14mm thick, a slim silicone case might be the only way. A flip case would add a lot of bulk. Wouldn't be a deal breaker though.
I would make the case definitely some sort of semi-transparent colour or matt black.
I use the Swiss layout which is quite similar to QWERTZ.
I think EskeRahn's solution might be the perfect compromise for all German speaking and Scandinavian people.
And if it could get shipped on the same date like the QWERTY version would be perfect.