I will play devils advocate (with the standard disclaimer):
English is the international language of Air traffic control. If I remember my history, it was agreed to by an international convention after WW2.
In Der Gross Schlag I was assigned to a group of 190s that were texting back and forth in Finnish... as I speak English, German and Korean but not Finnish, I was lost and ended up flying with a different 190 Staffel.
Recently I was up in the middle of the night (Pacific time) and was supporting 5 or 6 guys trying to take a base, all texting and speaking Spanish. Again I was lost dispite my schoolboy Spanish.
The greatest number of players are from English speaking areas and most players from the EU can at least read English... It would be kaos if there were 8 or 9 languages flying around on country/200.
This view in no way is meant to detract from the languages/cultures of my German/French/Swedish/Spanish/Russian/Farsi/Portugese/Finnish/Polish/Uzbek/Arabic/Italian/Inuit/Mongolian/Sanskrit/Latin/Chinese/Swiss or Canadian AH2 flying brethern (Yes, there are a couple of "ringers" in that list)
