It’s raining cats and dogs
In English-speaking countries idioms for heavy rain include it’s raining cats and dogs / buckets / stair rods / pitchforks / elephants & giraffes, or it’s pelting / chucking / pissing / tipping it down. In Australia some people say it’s a frog strangler, it’s a frog-strangling-gully-washer, or it’s a frog-strangling downpour.
The origins of the idiom, it’s raining cats and dogs, are uncertain. The most likely source is a satirical poem by Jonathan Swift, A Description of a City Shower, first published in Tatler magazine in 1710. The poem includes the lines “Drown’d Puppies, stinking Sprats, all drench’d in Mud / Dead Cats and Turnip-Tops come tumbling down the Flood.” There are more details here.
In other countries it can rain old women with knobkerries (Ou vrouens met knopkieries reen – Afikaans); boats and casks (Està plovent a bots i barrals – Catalan); wheelbarrows (Padají trakaře – Czech); shoemakers’ apprentices (Det regner skomagerdrenge – Danish); frogs (Il pleut des grenouilles – French); cobblers’ knives (Tá sé ag caitheamh sceana gréasaí – Irish); fire and brimstone (Það rignir eld og brennustein – Icelandic); female trolls (Det regner trollkjerringer – Norwegian) or knives and forks (mae hi’n bwrw cyllyll a ffyrc – Welsh).