"I want to go out."
Translation:Eu quero sair.
It's also acceptable. Some verbs+preposition in English are sometimes translated as just one verb in Portuguese. A few examples: look for = procurar, hang up = pendurar, look into = examinar... and so on. So, a more literal translation (ir para fora) is not wrong in this case. But it would be wrong to say "sair para fora" once said means "go out". If you "sai", in portuguese it's obviously to outside!