Imagine for a second the international language of planes was German. As an American who's an international pilot you of course speak German, although not as well as you speak English.
Now imagine you're a bush pilot flying around Alaska in a Cesna flying near Anchorage. Imagine being forced to speak German to your fellow American ATCs.
These aren't bush pilots. They're professional airline transport pilots. Their job requires a proficient level of aviation English.
I've never heard of the English rule being ignored anywhere else except perhaps at tiny airports without proper radio discipline. Though I was only a private pilot.
It's not that it has to be in English because it's meant to be a better language. It's because the international community chose it. English is a requirement because lives were lost because of this (think Avianca 52). Foreign pilots have to do a language test to get their license. Even for a PPL. At least here in Europe.
Also the phraseology of radio communication is pretty specific and even a native English speaker wouldn't make heads or tails of it if they have no knowledge of aviation. It isn't really English as such.
It's no coincidence that the French invented the word Chauvinism :) I the multinational company I work for I've never seen a people so angered at having to speak another language than the French.