People assume that once their English is good enough, friends will follow and belonging will take care of itself, as though language were the only key.
It does not work like that.
Two fronts at once
If you were already the quiet one at home, hesitant to speak up, used to sitting still because you were raised to be modest, then abroad you are fighting on two fronts simultaneously: the English, and that reticence.
Communication is not a skill that English hands you. The proof is that you can speak flawless Vietnamese and still fail to connect with anyone, if you do not know how.
English is only the tool
English is the tool. You are the one who decides how far a conversation goes.
So do not only learn the language. Learn what makes people want to talk to you.