And to all you native English speakers saying it's about "ethnocentric elitism" or such: Really, it's not. Nobody is saying "speak English or gtfo".
No, but you are. Maybe you don't realize it, maybe you think you're a cosmopolitan person because you *tolerate* other languages, but you're essentially saying exactly what you claim nobody is saying.
You said it yourself that it hasn't been BAD ENOUGH that a rule need be enforced. This implies that speaking anything but English is WRONG, and that if it reaches a certain boiling point, rules to the effect of "speak English or gtfo" would need to be implemented to bring the "problem" back under control.
That is ethnocentrism, whether you are willing to admit it or not. But don't worry, the colonial empires of the nineteenth and twentieth centuries didn't know that they were being ethnocentric either. And your attitude that you are willing to tolerate it to a certain extent is elitism. Thus: ethnocentric elitism.
As one of my favourite comedians (Jimmy Carr) put it, offence is generally taken, not given. If you find it rude and annoying that other people are speaking the language they know, the problem is yours, not theirs.
Finally, this idea of catering to whoever *might* be listening is just silly. How do you know that the majority of people on map chat at a given time are native English speakers? On my server, past 1am, there's a very good chance that the majority of users on a given map are Korean. Should we disallow all other languages but Korean between 1am and, say, 8am? Perhaps we should require hourly polling to determine the majority language?
Who decided that English was the official language of the world? It's not, it's an unofficial lingua franca. And enjoy it, because 30 years from now, you may not be able to use map chat in Guild Wars 8 unless you speak Chinese.