that you should learn a language for every country you plan to fly through
To me it seems like normal flight preparation to check for an a/d's useability before flying there - which includes making sure I either can talk to the locals, on the radio AND on the ground, or I won't need to. Just as essential as checking runway length, fuel availability &c.
Concerning en route R/T, I think English should be available at least in all of Western Europe, though the quality might be disappointing in some southern countries as has been reported on these pages.