I might add that the old German system seems to have been close to the Swiss system. Insofar that Turkish citizens living permanently in Germany could also apply for citizenship if they met the criteria.
Which were pretty high IIRC.
Language test, proof that you have renounced your "old" citizenship etc.

I´m not sure but I seem to remember that one additional problem was/is Turkish laws?
If you don´t/didn´t have Turkish citizenship, you could/can have inheritance problems in Turkey?