Thanks a lot for all your input.
After the hint to Hofner, I think it could be this model (1950s Hofner 456 Sunburst Schlaggitarre):
I remember, it had a darker color by the time I bought it. It did change that (probably not in a very professional way). I once even had to glue (donât know if this is the correct expression) the neck because the guitar broke into two parts during a rehearsal). A violin builder told me that would be too expensive (?! I was young and ignorant) and how to do it on my own. So I fixed it and it is okay until todayâŚ
Edit: The head has a somewhat different shape and matches more the 457-model.