The population of São Paulo is very diverse. Blacks, mulattoes, dark haired and blond whites, Asian, all races are represented in São Paulo. This is good for visitors, it is very easy to blend in with the locals (as long as you do not dress like a tourist).
The local language is Portuguese. If you know Spanish you will have no problems, either, communicating with locals. English is the most studied foreign language, but not everybody can speak it. In hotels and tourist places you will not have any problem. In restaurants, bars and shops, a Portuguese Phrase-book may be handy.