You can use
Klaus. It's a name, and has been for centuries. I have no idea why Americans can happily put up with, as you say, Haizleigh and similar horrors but reject
Klaus usw. Perhaps they don't!
May I suggest that you ask some teachers of preschool children how they would respond to a list of names that you'd show them; not all of them
German by any means. Then you'll at least have hard data to use.