Teammates not writing English = instant loss?

Hey guys, I experienced this so much but I want to know if somebody else thinks the same.

(This is on EUW)
When teammates start writing in any non-English language, they tend to be feeding, trolling or eventually afking. Especially French, German and Spanish players seem to be like that. It gets even more ridiculous when they start insulting you in their native language. I don't get it. If you really want to insult somebody, make sure they understand. Besides that, not writing English is a team communication killer. Give me any good reason, why it should be okay to write non-English in ranked games.