The majority of the population in Brazil won't say a word in english, so they would rather use a not so good app in portuguese than one in english... the refinement can come later as it grows in that market (and hopefully some users' feedback)
long answer: Most Portuguese users under 30 years old can read and write, at least, basic english, and would prefer to use the english version of your app instead of brazilian portuguese. This is the scenario that I experience with people around me, at least.
People who are not so comfortable with english will _endure_ the brazilian portuguese if you provide no alternative.