Portuguese is spoken all over Brazil by 99% of the population. No matter where you go, you will be perfectly understood by everyone around you, right? Wrong! You might be able to communicate well, but the dialectal differences among the different regions of Brazil will not let you perfectly understand others and be understood all the time. In this article, I do not mean to scare you or make you think that you have to choose Portuguese from a particular region of Brazil. There is a significant common ground in Brazilian Portuguese that all regions share. However, depending on where you go, it is important to know the different names for different things to avoid misunderstandings and embarrassing moments.
To illustrate, here goes an example from my own experience. I am from Recife, a city located in the northeast part of Brazil, and when I was 11 years old I moved to Rio de Janeiro. In my first day of class, I forgot my sharpener at home and needed to sharpen my pencil. I called one of my classmates and asked: "Você pode me emprestar sua lapiseira?" (Can you lend me your sharpener?). Immediately she handed me a mechanical pencil and surprisedly I said "A lapiseira" (The sharpener). She looked at me and said "Sim, você não pediu a lapiseira?" (Yes, didn't you ask for my lapiseira - she meant mechanical pencil). I decided to say yes and take the mechanical pencil...this would work anyway. After some days, I realized that in Rio de Janeiro and many states of Brazil, "sharpener" is called "apontador", not "lapiseira", and mechanical pencil is "lapiseira", whereas in Recife we call it "grafite".
In order to make you aware of these differences and at the same time expand your vocabulary, here goes a list of things that differ from region to region.
1. BISCOITO vs. BOLACHA: This has been one of our greatest fights of all time. No other words better illustrate the differences we have than the pair biscoito (/biʃ.kˈoj.tʊ/ or /bis.kˈoj.tʊ/) and bolacha (/bo.lˈa.ʃɐ/). In most states of the northeast of Brazil, biscoitos (plural form) are cookies, like Oreo. However, in most of the Southeast and South, these are called bolachas (plural form, although not commonly used in the plural). In the northeast, bolacha is like a cracker whereas in the southeast this is called biscoito. Got it? What is biscoito in the northeast is bolacha in the southeast, and the other way around. You might ask me about the central, south and north regions of Brazil...I am not really sure how they say it, but I believe they are not so involved in this fight as the southeast and northeast are. By the way, biscoito is a "masculine" word (o biscoito) and bolacha is a "female" word (a bolacha).
2. BISCOITO vs. SALGADINHO: Biscoito is such an intruder! This guy is also involved in another fight. This time, in some states the word biscoito is also used to refer to chips like Cheetos, while in most states of the northeast Cheetos are called salgadinho (/saw.gɐ.dˈi.ɲu/).
3. BOM DIA vs. BOM "DJIA": This is probably the first sentence you learned in Portuguese. Depending on where your teacher is from, the word "dia" is pronounced differently. I believe in most states, Brazilians pronounce dia as "djia". This is means that words like "diferente", "diagrama", and "pode" (because the "e" has the sound of an "i") are all pronounced like "djiferente", "djiagrama", and "podji". When I lived in Rio, many friends would joke with me because I would always say "Bom dia!" because that is the way we say in Recife.
4. JERIMUM vs. ABÓBORA: These two words mean "pumpkin". The word jerimum (unable to find the phonetic transcription, maybe it is less common) is used in most states of the northeast part of Brazil while in the southern region the word abóbora (/a.bˈɔ.bo.ɾɐ/) is preferred. In Recife, most people say jerimum and older people would use the same word for the color "orange".
5. PIPA vs. PAPAGAIO: These are two words that mean kite. These words may be more related to generations rather than regions of Brazil. My father would always say "empinar papagaio" (fly kites) and my siblings and I would say "empinar pipa". By the way, the word papagaio literally means parrot. I am quite sure the word pipa (/pˈi.pɐ/) is more common than papagaio (/pa.pa.gˈaj.ʊ/).
This is a really simplified version of all differences we have in Brazilian Portuguese. You may learn some more the more you get in contact with native speakers of Brazilian Portuguese. Learning these differences will help you to not only understand and speak Portuguese better but also to understand more of Brazilian history and culture, as these differences do not occur randomly and are mostly marked by the socio-cultural and historical context around them.