There is no way for a community to impose its language in a public channel because such channels are very local, if you talk in the game your words will reach the ears of the people around only. (There is the exception of the Founder's channel and the Waerd family channel)
Overall, languages are tools for communication. But as we have different in-game languages, it has been noted that there are way to communicate without talking, through gesture, and showing your intentions.
For cases where a talk is needed, English is indeed a nice tool to be understood by the majority. Considering that CoE is an English game (I think no translations are planned atm?), a player that can't understand English will either not be able to understand the NPCs or have a "translator" buddy who can help him through the dialogs. In the former case, it's like the player is missing a requirement to fully enjoy the game, as a 2 yo child will not be able to read text in a visual novel. In the latter case, the translator can still help establish the communication.
So, in the general case where a player is playing an english game, and understands enough english to understand NPCs, but still talk in a non-English language to someone who doesn't understand that language, that player is kind of refusing to communicate. If a french guy comes up to you, and start talking in french, understands that you don't speak french, and still talk in french, it's clear that his intent is not to communicate, with you at least.
Then language barriers can be used as ways to exclude people from the discussion. You don't speak french, welp too bad you'll miss half of what is being said. It's like they're whispering, without showing the intent of whispering. Even worse, they can be badmouthing you or tricking you right before your eyes, unless you are fast enough to google translate everything. That's one of the main reasons why English people tend to force their language to non English speakers in online games, since English is not only the most common "international" language and the game is clearly in English.
It can be quite hard to accept, why this language and not mine ? But a choice had to be made, to make international communication easier and more accessible to everyone, there had to be one language, and most of the time it's English.
So in short, another language than English taking over channels is impossible, I think that was the concern that brought this topic ?
And if someone if talking to you in a language you don't understand it's either English and you're lacking in the needed language to play the game or another language and the other person just doesn't want you to understand him.
(.. Until Mandarin becomes the international language)
(oh and I'm french btw, that's why I use french as an example a lot)