رضا: It used to be called "Proper English," but it's been awhile since I heard anyone say that. We just say, "English." The United States has no legal official language for most things, even though everyone says English is the official language. Someone wanting to become an American has to prove they know English, but if you're already an American you can speak any language you want to. And advertise in any language and exclude English from said advertising. Recently a city enacted an ordinance requiring English to be printed on a business's sign. It is being fought in court. I know Canada has such a requirement in Quebec, but that's a different country. I believe a business should be able to advertise in any language. If I can't understand their sign, then they're not wanting me for a customer. Seems simple enough to me. The only entity that I'd require to just use one language for official business is the government. Having a common language makes it easier for everyone here to know what to expect when dealing with the government and encourages people to know that language.