Driving licenses issued in another country must be either converted or exchanged 6 months after the holder has relocated to Germany.
An exception to this rule is when the license was issued in a EU member state and thereby remains valid. It also depends on the country or place of issue what needs to be done and we always check the status of the new arrivals. David was lucky, a driving test was not necessary as his license had been issued in Michigan (USA) and could be simply converted. We had submitted a request previously and today were able to collect European driving license at the motor registration office.
We wish David happy motoring with green lights all the way.