What are some negative consequences to declaring English the official language of the U.S?

English is the official language in most of the known world but no one declares it that way.

There was a time when english visitors to Quebec Canada found that communicating with anyone there wasn't an option if one didn't speak Québécois. It had become an unspoken rule in Quebec that english wasn't acceptable, for a time. It isn't that way now because their tourist trade suffered immensely.