A friend of mine is planning to travel around Latin America for some months, splitting his time between Spanish Latin America and Brazil, and asked me whether he should try to learn Spanish and Portuguese at the same time. I sent him a response and then thought I would post a slightly modified version of it here.
First, something I had said to this friend earlier in person: many travelers to Latin America seem budget rather little time for Brazil, e.g., a month out of a 6 months trip. I am guessing this might have to do with a desire to visit more countries. Please keep in mind, however, that Brazil is nearly a half of South America. (To be more precise, it’s accounts for 51% of population and 48% of the territory of the continent.) It is also easily as diverse r more than the Spanish-speaking half of the continent. So, unless money is a huge factor (Brazil is a bit more expensive than the rest of South America), I would suggest that a more balanced split between the two. If you are spending 5 months in South America, spend at least 2 in Brazil.
Now, on to the language.
First, Portuguese and Spanish are two very similar languages. They are especially similar in writing, and if you know how to read one you would read the other without too much trouble. When it comes to spoken language, there are two sources of differences. First, while most Portuguese words are spelled in a nearly identical way to their Spanish equivalents, they are often pronounced completely differently. To a Spanish speaker spoken Portuguese may be nearly incomprehensible at first. (A literate Portugeuse speaker would have less trouble with spoken Spanish.) Portuguese pronunciation is perfectly regular, but very is intuitive. It also varies a bit from one region to another. Spanish phonology is also more complex than Spanish, though this might be less important for a beginner. (You probably won’t hear the difference between ó and ô or between é and ê in the first few months anyway.) This has an important implication: you can learn Spanish without an audio course, but you can’t easily do this with Portuguese.
Second, formal Portuguese/European is very similar to Spanish grammatically, but colloquial Brazilian Portuguese has has a rather different grammar. Unfortunately, you won’t find a course that would teach you “real” Portuguese, since most educated Brazilians are in denial about the language that they actually speak. (They will tell you that they don’t use certain grammatical constructions while using them in that very sentence.) Formal Portuguese grammar is also somewhat more complicated than Spanish grammar. This has another important implication: unless you are planning to use Portuguese for serious writing, learning formal Portuguese grammar is a giant waste of time: you would be spending a lot of time learning grammatical forms that nobody practically uses.
For someone who wants to learn basic Spanish and Portuguese for traveling with Latin America, I would recommend with a combination of a Spanish course oriented towards vocabulary and grammar and a audio course for learning basic Portuguese. In other words, try to learn Spanish “properly”, but for Portuguese focus on familarizing yourself with pronunciation (this is very important), and learn the basic vocabulary – those words are often different between the two languages and since you use them all the time, it’s good to know them. Apart from that, work on the assumption that (a) Portuguese grammar is basically the same as Spanish, (b) all complicated Spanish words can be used in Portuguese as long as they are Portuguesified slightly. When you get to Brazil, you will probably pick up more vocabulary and some colloquial grammar. Knowing colloquial Brazilian grammar helps, but Spanish grammar will provide as much of a foundation for it as the formal Portuguese grammar that you would be taught in a Portuguese course. And much unlike the formal Portuguese grammar, Spanish grammar is something you will actually hear live people using in Latin America. (This is all assuming you are traveling to Latin America – formal Portuguese is spoken in Portugal.)
What about learning the two languages at once? Would it get confusing? From my own experience, yes, it is hard to keep them apart, and if your goal is to learn good Spanish or good Portuguese then the other language will get in the way. On the other hand, if you want to simply get bye in Latin America, I don’t think it’s that big of a deal. My impression is that most of Latin America treats is willing to give a breat to speakers of “Portuñol.” Some people seem to even embrace this mixture as a symbol of Latin American brotherhood. You will have to mind some words if you don’t want to end up embarrassed (incidentally, “embarassada” would be one of those words), but other than that, few people will complain too much if you insert some words from the other language.