OK linguists explain this

[warshipadmin]

OK there's motyl/metalyk/Matyliok and flutur/Fluture, but other than that it's anarchy. I've just checked and the welsh may have 3 words for them

Iâr fach yr haf - butterfly

This is one of the Welsh terms for butterfly, and would be literally translated as small hen of summer. But another one is glöyn byw - the translation for which is live coal. And there's also pili pala, which Dr Tovey explains, is "cognate with 'papillon', so has proper posh Latin roots".

[Micael]

It’s an interesting one for sure. I suspect that there’s more of them that has a common origin though. The ”fjäril” in Swedish for instance seems to have the ending part come from the same origin as the latin papilio, and the beginning part probably comes from getting part of the word fjäder (feather) attached to it at some point. So it’s effectively a half-cognate with the French papillon.

I kind of also wonder if motyl/metalyk/Matyliok isn’t related to ”moth” in some way.

[Jotun]

Butterfly and Schmetterling could have the same folkloric(?) source. An old European folk myth says that witches turned themselves into butterflies to steal milk or milk products like cream. Schmetterling thus may come from the Czech word for cream (smetana). Butterfly is self-explanatory.

[Zen9]

Quick observation. I thought Butterfly was originally flutterby.....which of course is what it does.
I'll have a ponder on the rest....