So, I solved my last problem. Deleting the registry entry of NLS_LANG solved the problem. After this, the open database also showed me the NLS error again. I decided to start again with another environment, maybe the source was the problem ;)
With a new set, I ran into another problem...the database service cannot be started.
DIM-00019: Create Service Error
The Oracle Service service terminated with service-specific error 997
So, why can't I create this service anymore ???
It does create an entry in the registry....