Pineapples and butterflies: two nice things, two odd words. Pineapples are neither pines nor apples. Butterflies are neither flies nor butter. But never mind that. Look at this:
Portuguese (European): ananás
Hungarian: lepke, pillangó
Okay. So we have two big questions.
First, why does almost every European language but English call a pineapple "ananas"?
Second, why do they all have completely different words for butterfly?
The short answer: History and fantasy.
People in Europe had never heard of pineapples before the early 1600s. When the European invaders of the Americas brought the fruit back to Europe, they brought a word for it, too, same as they did with things like tomatoes and avocados. And the word, taken slightly changed from the Tupi language, was ananas.
So why didn't English go with that like just about everyone else did? We decided instead to use a word we already had that previously referred to pine cones. It's pine because it's spiky and apple because it's fruit. (Hey, French calls potatoes "earth apples" — pommes de terre.) We did use "ananas" a little bit back in the 1600s to 1800s, but pineapple prevailed. The fact that the word banana came over from West Africa (from the Wolof language) in the later 1600s probably helped pineapple win for clarity. Other languages didn't have another word to use, so they just stuck with ananas.
Butterflies, on the other hand, have been all over the world since before there were even people. They weren't imported all at one time. But that still doesn't account for why practically all of the different languages' words are different from one another. Words within language families tend to resemble each other. Butter, in the languages listed above, is beurre, burro, mantequilla, manteiga, Butter, boter, smör, smør, maslo, masło, voi, või, vaj, boútyro. Just five different sets of related words. Look again at the words for butterfly: 15 languages, 15 entirely different words — 16 when you count English. The words for "butterfly" have done about as much fluttering around through history as butterflies have.
So what accounts for this chaos? Witches, women, souls, birds, flowers, fluttering, and mists.
First come the witches. Some Germans at one time had the idea that witches turned themselves into butterflies to steal cream. The word Schmetten means "sour cream" in an Austrian dialect (taken from Czech smetana). From that they apparently made the word Schmetterling for those pretty little witches.
If you think those Germans are funny, guess where we got butterfly from. Yup, it may well have been because we thought they were witches coming to steal the butter. Or it may just have been that people thought butterflies liked butter, or that some of the more common ones in England have pale yellow wings. Or it may originally have involved beating (of wings) rather than butter. What we do know is that it doesn't come from flutter by — the Old English word for butterfly was buttorfleoga, which is too far to flap from flotora be, Old English for flutter by.
Then come the other ladies. Russian for butterfly is babochka, which is a diminutive of baba, "old woman." The story goes that Russians believed that women turned into butterflies when they died. Witches especially. Meanwhile, Spanish children used to sing songs that included verses such as "María pósate, descansa en el suelo," which means "Mary, alight, rest on the ground." From María pósate came the Spanish word for butterfly: mariposa.
Next come the birds and the flowers. The Danish sommerfugl means "summer bird." They have actual birds in Denmark in the summer, too, but there it is. Meanwhile, the Greek petaloúda is related to the word pétalon, which is the Greek origin of petal. So in Greek, butterflies are seen as like flying flowers. Which sure beats witches who steal butter. But in ancient Greek, they used the word psyche, which also meant "soul" — more dead people fluttering around.
And, yes, there's the fluttering: Several of the words in other languages come from imitations of the butterfly's fluttering wings. The ancient Romans thought papilio was a good imitation of the wings flapping. French papillon comes from that, and Italian farfalla and Portuguese borboleta may as well — or borboleta may actually come from Latin for "pretty little thing." Dutch vlinder may be related to a word for "flutter" and may be related to an older imitative word viveltere, which comes from an older Germanic word that may be what developed differently into Swedish fjäril (or fjäril may be related to feathers).
Talk about words fluttering through history. English also has a related word, flinder, but we decided we liked butterfly better — just as the Germans preferred Schmetterling to Feifalter. It's the witches, I tell ya.
And then there are the dark mists of time. The Estonian liblikas and Hungarian lepke are descended from a single Finno-Ugric root, as is an alternative Finnish word, liippo. We're not sure where that root comes from, though it may be borrowed from a Greek word for "scales" (which you'll also see at the start of the genus name Lepidoptera). We are less sure where Hungarian pillangó and Finnish perhonen are from, aside from perhonen being a diminutive of perho, which also means "butterfly." Southern Slavic languages tend to use leptir or a similar word, which may be from the same root as lepke. Some Slavic languages have a word like the Polish motyl, coming from a root that may have to do with sweeping (as in back and forth) or may be related to...um...excrement. Small wonder that the Russians preferred their little old lady babochka.
Pineapples, meanwhile, just sit there. They may be delicious, but they're not magical like butterflies.
Incidentally, in many languages, they use the same or a related word for moth as for butterfly. Some languages call moths "night butterflies." Well, they are closely related. And some languages, such as Italian and Russian, use the same word for bow tie as for butterfly. You can see it, right?