I wonder

depends on the server, i used to play on the euw server and a majority were able to speak english but there were a good number who only spoke their native language or just didnt speak english. My guess is that english is only dominant on na because mostly americans and canadians play. i have encountered mexicans and since i speak spanish it wasnt difficult to communicate with them. Also the clients language nomatter what server can be changed so the only difference will then be the languages your fellow players speak and if you dont speak the same language pings are universal