The Amsterdam scenes were mostly filmed in the "Holländischen Viertel" (Dutch Quarter) of Potsdam. Though most cars had Dutch license plates attached to them, there's one with a German license plate with the P from Potsdam.
Since it is possible to drive from Potsdam to Amsterdam in a reasonable time, a single German Plate could be a tourist.
The scenes taking place in Amsterdam were actually shot in Potsdam (near Berlin); the Dutch Quarter. In spite of all the Dutch number plates on cars and Dutch street names (Tolstraat) you can clearly identify the restaurant "Zum Fliegenden Holländer", Benkertstraße Potsdam. Also, most Dutch number plates are fake and out of sequence of the normal numbering of Dutch plates. Although the license plates have the correct colors (yellow for personal cars and blue for taxis), they have too many numbers and letters on them.