Turkey recently had presidential elections and apart from around 62 million Turks living in Turkey people with Turkish nationality but permanent residency in some other country were eligible to vote. The biggest such group is in Germany with approximately 1.5 million people eligible to vote, approximately half of them actually voted (source).
Suppose the German government wants to prevent these German residents from voting. How could it legally achieve that?
The people in question have Turkish nationality and either a permanent residence permit for Germany or additionally German citizenship. Their primary residence, place of work, school etc are all located in Germany. The voting happened in Turkish embassies and consulates located in Germany.
Measures that only work for most people would also be interesting. Discussions on whether the German government should or shouldn't do that are opinion-based.