Germany is one of the five locations featured in both Spec Ops II games, Green Berets and Omega Squad. It does not need to be completed in any order.
There is also a German flag in front of the hotel where Riggs and his Refugees is holed up at the beginning of Chapter 10.
In Chapter 4, there is a German translation of the sign reading "Keine Waffen im Lager", which translates correctly to "No weapons in the camp".