Several languages have this. Spanish has the Real Academia Española (RAE) and French has something similar.

But they're not generally in much of a different position than a dictionary is. If the people start using the language in new ways they have little recourse other than to accept it and amend their rules. If they refuse they'll look antiquated and people start to question their influence.

They certainly do have influence of course, but the ultimate authority is the people who speak the language in the end.