“To look for a needle in a bottle of hay”, after the french botte for ‘bundle’.
On the odd use of bottle: [Puck, to Titania] I could munch your good dry oats, methinks I have a great desire to a bottle of hay: good hay, sweet hay, hath no fellow.
Interestingly, haywire is derived from a frenzied behaviour likened to the chaotic uncoiling of a feel of hay baling wire.
cercare un ago in un pagliaio
literally
looking for a needle in a haystack
or sometimes:
trovare l'ago in un pagliaio
literally
finding the needle in the haystack
the meaning is slightly different, the first is more about describing something vane, the latter is more about describing something very, very difficult or nearly impossible but that by luck or some other reason actually happened.
For the record, I believe there is very little typically Romanian in that way of making haystacks, many, many years ago (before the machines came) haystacks in Italy were made with the same techniques, maybe they actually date back to theRomans.
https://www.expressio.fr/expressions/chercher-une-aiguille-d...
(also provides equivalent expressions in several other languages).
In German it's pretty much just the literal translation of the English phrase and its variations: "(Wie) die Nadel im Heuhaufen suchen" - (like) looking for the needle in the haystack, etc.
"Como buscar/hallar una aguja en un pajar" (like looking for/finding a needle in a haystack) means taking/achieving a nearly impossible task.