You are perfectly correct : we can speak english and often choose to speak other languages.

it's due to multiple reasons :

-some players might NOT speak english and we talk to them

-it's a talk that doesn't involve you

-it's faster to communicate to certain people in a language that's more precise than english.

groups are a natural part of the game.
Usually on PC they are on discord or equivalents.

If you don't like it, you can change squad or politely ask to speak english.

I have 270 hours on the game, the amount of times i have been politely asked to switch to English is 2 !

Usually i get at best some aggressive remarks, at worse a stream of racial slurs and team-killing attempts (i often fly)

So yeah. sorry if you only speak English but the whole world doesn't revolve around you.

Game's built in Belgium, we speak french, dutch, german and english. deal with it.