Knowledge of any Romance language automatically offers learners a leg-up when they undertake the study of another language in that family; however, those with a solid base in Spanish have a particular advantage when it comes to studying Portuguese, given that the two languages share a great deal of vocabulary and similar grammar. While linguistic differences certainly exist between Spanish and Portuguese, language learners with a strong background in Spanish will find obtaining fluency in Portuguese to be a very attainable goal (and vice versa for Portuguese speakers).
Linguists have determined that Spanish shares an 89% lexical similarity (the degree to which the word sets of any two languages are similar) with Portuguese, and, overall, the two languages exhibit a fair degree of mutual intelligibility, roughly 50% according to one study. With such a large chunk of shared vocabulary and closely related grammars, those with Spanish fluency can read and understand a significant portion of a text written in Portuguese, although understanding the spoken word presents a greater challenge due to considerable pronunciation differences.
Spanish speakers studying Portuguese must make an effort to avoid two main mistakes. First, while the two languages do share quite a bit of vocabulary, they are also rife with false cognates (also known as false friends). False cognates can make for some rather confusing (and occasionally, entertaining!) situations. Don’t fall for them—make an effort to memorize which words are false friends. Second, avoid lapsing into portuñol, the dialect best described as a mix of Spanish and Portuguese. Spanish speakers just beginning their Portuguese studies may be tempted to use Spanish pronunciation, grammar constructions or vocabulary when their Portuguese fails them; however, it’s important to respect the differences between the two languages and keep them separate.
Check out the website Tá Falado with podcasts and lessons geared toward Spanish speakers looking to learn Brazilian Portuguese.
Examples of false friends
|Acordar: to wake up||Acordar: to remember, to agree|
|Ano: year||Ano: anus|
|Apelido: nickname (Brazil)||Apellido: last name|
|Barata: cockroach||Barata: cheap|
|Borracha: rubber, eraser||Borracha: drunk (female)|
|Cena: scene||Cena: dinner|
|Esquisito: weird, odd||Exquisito: delicious, exquisite|
|Fechar: to close||Fechar: to date|
|Oi: Hi||Hoy: Today|
|Largo: wide||Largo: long|
|Latido: barking||Latido: heartbeat|
|Logro: fraud||Logro: success, achievement|
|Mala: suitcase, bag||Mala: bad, naughty (female)|
|Ninho: nest||Niño: child|
|Osso: bone||Oso: bear|
|Polvo: octopus||Polvo: dust|
|Saco: bag||Saco: jacket|
|Salada: salad||Salada: salty|
|Solo: soil, earth, floor||Solo: alone, lonely|
|Taça: wineglass||Tasa: valuation, tax, rate|
|Tirar: take, remove||Tirar: to throw|
|Todavia: but, still, however, notwithstanding||Todavia: still, yet|
 Source: http://en.wikipedia.org/wiki/Lexical_similarity#Indo-European_languages
 Source: http://www.sulajohn-translations.ws/files/users/e/535D6469E2612048E040A8C0AC002D4E/Mutual%20Comprehension.pdf