The language of the keyboard should be changed with the locale/language setting in openhabian-config. Do not use raspi-config, it will not help. Better check here for the complete answer: https://wiki.debian.org/Keyboard
Besides that: You are trying to make your german keyboard work, which tells me that you are trying to work with the RPi by actually connecting a display and a keyboard. That’s not the ideal way. You should consider working on your powerful PC via SSH, giving you many benefits while the relatively weak RPi can sit in the shelve/corner.