english is the main/primary language. spanish, chinese, etc., are just secondary languages, you don't have to know spanish to live here, but english is more preferred.
Though the US doesn't have an official language, I think it's more a policy that makes us look good.
English is definitely required to be successful in the US, but it sounds better if we don't say that.
However, Spanish is certainly a secondary language, and Wikipedia also lists French (the current lingua franca, I believe) and Hawaiian.
I would love the US to develop into a more bilingual society, much like that of continental Europe. But nationalism runs high here, so any deviation from the norm may take a while to be widely accepted.