Yes, you can use a prong collar in Germany. The German Animal Welfare Law (Tierschutzgesetz) prohibits measures that cause significant pain, suffering, and damage to an animal. Thus it depends on how you use the prong collar. But the collar per se is allowed.
It is illegal in Switzerland and Austria though, with the exception of working police K9s.
German native here.
Chip v. Dog Pound (border terrier), CGC
Elly v. Rescue (GSD, GSRNE 346), HI(C), CGC, TT
RIP: Feli, Iris, Dago (GSDs), Bubi (spitz), Tanja and Robin (mutts)