I agree with your basic sentiment-that English is (or at least should be) the primary language. However, if the stop sign remains a red octagon, I don't think it matters what you write on it. Stop signs in Quebec say "arret," but English-only speakers know to stop. (For that matter, stop signs in France say "stop," but French speakers know to stop.) Florida and Arizona (probably most states in the US) have vast numbers of Hispanics who do not spreak or read English, yet there is no huge problems with car accidents caused by people who can't read the word "stop" on a red octagon sign. (For that matter, traffic lights don't have any words on them.)