My husband (brazilian) also uses "amargo" for sour... so I guess you could translate it as bitter/sour. It always confused me cuz sometimes I would like to differentiate because there IS a difference between sour and bitter :)
Technically, the word for sour is "azedo" and the difference between "azedo" and "amargo" is the same as the difference between sour and bitter. People do mix them up, however.