Common is weaker than official, but neither means much unless Congress explicitly defines what having an official language means. Without a definition, the executive branch has broad authority to interpret it's meaning, and it wouldn't really change anything.
Even if Congress does define it well, there's still going to be a good chance of it being undermined through judicial review in the name of preventing racism.
It needs to be a made the official language through an Amendment to the US Constitution which defines the scope of the official language as well.
I'd be all for an amendment.