I think any loud, short response paired with a pinch or "knock down" will work. The point of the loud response is to mimic a dog bark. Even when they are adults, if dogs start to play too rough one dog will signal they want it to stop with a sharp bark and nip.
"Ow!" just happens to be the word that comes quickest and easiest for me in that situation. I know I should mark the behavior I don't want as quickly as possible with a "bark and a nip" so that she learns. But, you could say "stop" or "no" like everyone else.
When I say "go pee pee," for Mishka it means urinate or defecate. I probably should have started off saying "go potty" instead. But I started saying "go pee pee" and "go poopy," then later decided two commands for going to the bathroom was too complicated. Since I was saying "go pee pee" more often, I just switched to saying "go pee pee" to mean "go potty."
You can train your dog with whatever words you want. Sie können deinen Hund in Deutsch trainieren!