As someone who speaks German, it feels puzzling to me why I would teach my dog German commands (even though I have a GSD), these are just the regular words/phrases for things but in a different language.
its a weak authentication. if you use a dog for work/husbandry, law military, it does two things.
1] regionally unfamiliar language, dog will obey your commands, but not commands of regional language.
2] parrallel handling, different dogs trained in different languages dont step on each others task,in response to the same cue command.
e.g. left dog, sprech im ze deutsch - right dog, govorite po russki
It's better with dogs to use commands that sound harder for hard commands - stop, down, wait, etc. Which German's love of crisply pronounced consonants tends to lend itself to.