Please read carefully the document referred to by Birgit, as it really does explain the German rules from the EStG very clearly.
The specific rule here is that if your client is a business (i.e. not a private individual) located outside Germany (irrelevant if EU or non-EU), you do not charge VAT on the face of the invoice because of the presumption in the EStG that the service (translation or interpreting) is rendered at the client's domicile, and not where the service is actually rendered
Despite what others may claim....
I agree with Robin, and it's also how my accountant has explained it to me. I only charge VAT to customers in Germany.