Went searching for an onomatapoia thread and found this old one - this is something I've wondered about Irish since I learned years ago that a frog says "kwak-kwak' and a cow says "booooo" in Dutch. You would think this is prime material for teaching young kids but I never remember it coming up through school.

My small contribution here is I believe that the post earlier in the thread that ducks say "bhac bhac" can be confirmed in the lovely sean-nós song An Lacha Bacach:

https://www.youtube.com/watch?v=YHa4jv7uOLo

https://songsinirish.com/?song=an-lacha-bacach-lyrics

Tar liomsa im’ dhóid
Chun go dtomhaisfead do chneá
Is ná bí chomh glórach ní ceol do bhac bhac
Idir bhriseadh `gus leonadh tá ainnise mhór ort
Is is céasadh san domhsa mo lacha bhacach.