I am not sure whether it technically matters in SchH, what language you use.
I like using German commands for formal obedience. I use English for informal communication.
For example, "Go lie down" means "pick a spot, lie down, and get comfortable". "Platz" means "hit the deck NOW right where you are!!"
"C'mere" means, "come my direction". "Hier!" has a totally different inflection and it means "Get to me quickly and sit in front".
Having a set of formal German commands also gets the dog in the right frame of mind for training, trialing or working. The same can be said of English, however--by simply using a different inflection and emphasis than that of everyday speech.
I do find that English commands can confuse a dog if they are used too frequently in everyday chatter. I never use the word "Okay" for training, for this very reason. I use "Free" as a release word.
I do use the word "No", but it doesn't have the same intent, meaning, or impact as "NEIN!!" "No" means "try again". And you know what NEIN!! means!