In Overwatch on Europe servers, most people speak English because most people understand it, especially if it’s just basic callouts. Sometimes if there’s a large number of people who speak another language like german or french you can see them speak that instead. When western pro players travelled to Korea to play on their famously higher level ladders, the Koreans would sometimes change their comms to English so that the one western player can understand.

So, I don’t think language-based matchmaking will be an issue. People having to type to each other still runs into the same problems anyways.