i don't understand why this even bother you. Someone tried to talk to you in language A. You answered in language B. None of you knows each other language. No point in continuing conversation. He left the chat. You move on with your day. I don't think he did something rude.
I think having more people in the server is better. If the majority of the population are non-english speaking people, If that's the reality, then you'll have to accept it or you can leave. You can't expect all of them to start speaking in English just because you prefer that. There's no written rule that you have to speak in English in ROT/ROEXE. If you can't be bothered to try to understand them, just ignore them. Having non-English speaking players doesn't reduce the number of english speaking players in the server.
Non-english speakers use the same RO client. Their UI, item and skill names are all in English. They should understand when you use these phrases.
Buy/Sell>"item name/link" "price"
Recruit Party>"class/role/all" "lvl range"
Need party>"your class & level"
Agi bless/heal/resurrection or "skill name" please
even share please
We use those with other english speakers. The respond to all those phrases, if you ignore all the small chat, are either yes or no / do or don't. And if someone type something you don't understand and you don't know how to respond, just leave it that way. It's really not that big of a deal.