The French are singing this nice liberation / freedom song against the germans. This is nice and all, but they are in freaking occupied Morocco, not France! They continued to occupy it even after the war.
The people that made the movie didn't care about this irony because they didn't consider moroccans to be equal to the french. I get that. What I'm surprised is that people nowadays don't find this scene ridiculous (or at least very ironic). Coming from a colonized country (and being one of those people that weren't considered worthy of having their own country back then), I can't like that scene.