If you have a foreign driving license that was not issued by an EU or EEA state, you may use it in Germany for a maximum of six months. After that, the driving license must be converted into a German driving license.
If you have a driving licence from another country in the EU or EEA and live in Germany, you must have your driving licence converted into a German document under certain conditions (e.g. if an extension of the driving licence is necessary).