Most Brazilians only have one common word for pineapple, [o] abacaxi. Like the English term, this one is an oddity versus the names picked by a series of other languages, which borrowed the term Ananas from Portuguese [o] ananás (which in turn came from Tupi nanas). In Brazil, [o] ananás is used in some regions for pineapples of inferior quality, or for sweeter pineapples.
In Portugal, both of these terms are commonly used – in fact, if you go to the fruit section of a supermarket you may see both ananases and abacaxis being displayed, and a variety of different pineapple by-products contain each of them. Many people disagree on what the difference is: [o] abacaxi is a sweeter variety, while [o] ananás is slightly tarter and acidic; the first is usually imported from the tropics (especially from Brazil), while the second is homegrown (in greenhouses or in the Azores); the fact that is a niche tends to make ananases more expensive, but that’s not usually a given.
If you ever find yourself shopping for pineapples in Portugal, just take a look at the location where they were harvested from to make a polite guess on how they will taste! You can also use your Portuguese skills to ask the grocer about this difference – maybe he will have a better answer than I do (:
When in doubt, use [o] ananás; that’s our own word, so we should stick to it when making general statements (: