A communication language is the language that is understood from both, seller and buyer.
If your CSRs do not understand German then it is probably the wrong communication language in the customer master. It is a common mistake that people enter the language that is spoken in the country that is entered in the address.
Moderator message: a subject in a discussion is like a headline in a newspaper, it should be interesting and to the point and make the reader curious. Putting the whole question as subject is not the way a subject should be used.