Just my 2c worth here as a monolingual pilot who was once told never to take a French class ever again but can order a beer in 7 languages.
When flying for my operator, I fully expect that, per the internationally accepted standards, that I will be able to communicate in English no matter where I am dispatched to within controlled airspace. With that being said, I also understand that there will be the possibility for local language(s) on frequency. I expect, however, that I will be provided any pertinent information from those local conversations - as someone pointed out, whether an aircraft cleared the runway I am about to land on. Furthermore, I fully expect that any emergency transmission I make will be understood by every pilot.
Now, were I to privately trek off into some Swiss valley (as another poster alluded to), I would think it best to do some due diligence and find out if they actually spoke English locally. If they did not, I would at least try my best to figure out the basic lingo for the area.
The fact that English and French are the only two "official" languages of aviation are a happy coincidence to aviation history. Had China figured out how to fly 2,000 years ago or had Germany won the war, it would be a far different story. In any event, it benefits some and not others.