Please be sure to check early on with the embassy or consulate of your destination country for any requirements you might need to meet to enter your destination country, and also to reside there for the duration of your internship. This is especially important if you are not a citizen of an EU member country. Make sure to resolve all affairs related to this matter before beginning your internship.

Furthermore, you need to check with the responsible Foreigners Registration Office (Ausländerbehörde) where you are registered at, to find out what you need to do to be allowed to re-enter Germany after your internship has ended.