In the Turkish airlines website it is stated that
Passengers are required to submit a negative COVID-19 PCR test result, taken within the last 48 hours, prior to arrival in Germany. Passengers who fail to submit these test results are not be permitted to board the flight. Passengers under 2 years of age are exempt from this application.
The PCR test may be taken at the organizations listed on the related website by the Ministry of Health or at airports with testing facilities.
However, what they don’t tell you in public is that, for example, in the capital city Ankara, there is only a single hospital which has the testing capability and gives the test results in less than 48 hours.
Plus, the tests aren’t free, you have to pay 250TL = ~30Euros.
So, if German a German citizen wants to return home from Turkey, does s/he need to take the test in order to go back to Germany? What if they can’t due to not being able to find any hospital who gives test results less than 48 hours? What if they take the test but the result haven’t announced, can they still board the plane?
After all, in Germany, anyone flying from a risk area can and needs to be tested at the border control free of charge.