Please, write in English, because we're still learning Portuguese.
Approximative translation: In southern Brazil and Mercosur "ananás " or "nana" is generally used for the wild pineapple (more acidic) or the cultivated one with low quality. The term "abacaxi" is used for the harvest of fruit of better quality, sweet and with low acidity.
Very interesting, it's fascinating than, for a same word, you have sometimes 3 totally different etymology, for example Boy/Girl etymology:
Menino/a = From the Spanish "men" (small, latin "minus") + "ino/ina" (affective suffix)
Garoto/a = From the French "garçon" = boy.
Guria = from the Tupi "Guree".
Pineaple is what it means. Don't try anything different from that.
But in Brazil, we have a slang using the pineapple as a problem.
Eu tenho um abacaxi = I have a problem
And you could use the cucumber (pepino) for that as well.
Also the hot potato (batata quente).
Probably because the pineapple is a thorny fruit, hard to handle. But I can't explain why the cucumber.... The hot potato is from a game where people throws the potato to the others until the music stops. The one with potato in hands at that time loses.
I think I can maybe explain the "pickles" one.
The abaxi one is obvious, an abaxi is thorny, it's a good metaphor for a problem. But I don't see the direct link between the English pickles expression and the cucumber. It's very unlikely than one expression could pass in another language being translated from "pickles" to "cucumber". I think a better clue is here:
The French word "pépin" means "problem" too, (but it doesn't mean "cucumber", it's a small seed.) This little seed can be trapped in gear (as in the maritime slang), and causes a snag, or you can swallow it, and it can go down the wrong way. "avoir un pépin dans le ventre (to have an apple seed in the belly), was also a slang synonym for = "to be pregnant"), and it's maybe also one of the reason why it became "to have a problem", because in the slang context it was used, it was not supposed to be in wedlock.
For "pepino", the expression is not rather "resolver un pepino"? (to solve a cucumber/problem)
There's also the expression "Descascar um abacaxi" (to peel an pineapple) = to solve a difficult problem or to be with an annoying person.
And I found also: "Estar com un abaxi/ Pegar um abacaxi” (to be as a pineapple/to take (?) a pineapple) = to have big troubles.
While "abacaxi" seems to be often a negative things when you used the word in a metaphor, I think it's very bad Duo gives use these kind of hint, if it collect all the expression with "abacaxi" and add all the words to the hints, we'll make it though with a good headache (an abacaxi, lol)
With some attention, in a slang context, yes. The "pepino" can also be interpreted as all long and cylindrical vegetables can....know what I mean?
Meu carro tá (está) com um pepino no motor = My has a problem in the engine.
Differences between "abacaxi" and "pepino" is that "abacaxi" is a really complicated problem.