First, I am not in Germany and can't speak German. My time zone is gmt+11 and i think it should work during the jam. 

If you don't mind these two points, you can take a look at what I can offer.

Some that I can offer the team

Efficient and positive communication (good at listening to ideas and improvements)

Overall game design ideas (level design, numerical design)

Enough experience in playing various games as reference (steam library 700+ games)

Project management 

Experience in game design (one year +)

If interested feel free to contact me, my discord username is error1931