Here we use english for all IFR flights, and danish for VFR if initiated by the pilot.
Often most VFR pilots will use english anyway, and for the normal daily routine we're never really experiencing any problems.
Sure a few "not so well" english speakers come by now and then. They're allowed to be here as well, and I don't mind helping them if need be by speaking slower/more clearly/staying away from non-standard.
Wonder how you manage to keep track of who speaks what langauge in a bilingual airspace? And I could see problems if you had to deliver a message rapidly, avoiding action as an example, and in the heat of the moment lost track of who spoke what langauge?