It’s less of a language issue and more of a bigotry issue. Look at your English as an example. You are fluent. I’m borderline fluent in Spanish, and I agree that (Brazilian) Portuguese is a VERY different language. However a lot, and I would argue most, players here speak English. Even if they don’t, it’s rarely a huge issue. It’s the blatant hatred between the 2 groups that is a real problem.
Also, no one is saying you couldn’t transfer to the English server if you wanted to. HOWEVER, if you start spamming in Portuguese in the English world chat (or vice versa), expect people to be mad at you, and rightfully so. One server would be dedicated to one region, and the other to the other. It would eliminate a lot of stupid arguments and hatred. That’s the major goal here.
The Latin American server would probably end up being a primarily English based server too ironically. The real issue is just the racism and xenophobia between the two groups. It has very little to do with language. That is more just an added bonus.
Once LevelUpGames releases their Brazilian version, I would argue that there might even be more non-Brazilian Latin Americans on the Latin American Steam Servers than Brazilians themselves. That would be hard to prove currently though, and is just a guess.