Dogs speak body language. It may be silent, but it is universal -- dogs everywhere understand it. People speak many languages, and a dog can learn to understand any of them as long as their own language is part of the conversation.
Sprechen Sie Deutsch?
If you can speak German, your German shepherd dog can learn it, too. Six useful basic dog commands in German are hier (come, pronounced just like "here" in English), sitz (sit), bleib (stay, pronounced with the long i sound of "eye"), platz (down, pronounced "plots"), fuss (heel, pronounced "foos" -- German for foot), and pfui (pronounced fooey, meaning nodamndogbadgirlstopthatdropitgetoff). There are lots more, such as komm (come), gey (go), hupf (jump) and box (crate). German is a good language for giving dog commands, as the words are usually simple, short and easy to put some oomph into -- use your "I mean it" voice. It doesn't have to be loud, just clear and emphatic.
Do You Speak Dog?
Dogs read other dogs' body language, but they have a hard time with people's because we're handicapped. We can't wiggle our ears properly and we have no tail at all as far as they can see, so our ability to express ourselves in dog language is limited. Instead, they have to rely on the strange noises we make. You can say fass in German or bite in English -- just be sure she knows what's expected when you do.
German Hand Signals
As long as you're teaching your dog German commands, you might as well teach her the German hand signals to go with them. Oops, sorry -- there are no specifically German hand signals for dogs, and no official international ones, either -- just whatever you and your dog agree on together.
It Pays to Be Multilingual
Teaching your dog commands in German gives you assurance that she will be less likely to confuse your orders with anyone else's if you are, say, at a very busy dog event. Also, the burglar in your house at 3 in the morning will be unlikely to know the command "aus" (pronounced like house without the h and meaning out, off or leggo my ankle). Unfortunately, neither will the meter reader in your back yard at 3 in the afternoon. Once your dog knows commands in German, don't try to add the same ones in English -- if you can't find a German one, try another language.