In English it could either be raining cats and dogs, a turtle floater or a frog strangling gully washer! But in Europe it seems the most common to remark on the heavy rain as from buckets, basins, tubs and jugs, though the Czechs get a bit pushy with a wheelbarrow. The Dutch and Swedes speak of rods and pipe stems. Much like the French, Germans and Turks with ropes, cords and strings, and the Greeks with chair legs.
The Afrikaans may have personalized the Welsh (old ladies and sticks) with Ou vrouens met knopkieries reen: it’s raining old women with knobkerries (clubs).
But I really enjoy the Swiss German: Es schiffet wiä d’Sau! because of the historical reference for schiffet: In olden times, noble women didn’t wear undergarments (gasp!), and when they needed to urinate, servants gave them a container shaped like a little ship (Schiff is German for ship). So the English translation becomes ‘pee like a sow’.
More humorous examples:
Catalan: Està plovent a bots i barrals / it’s raining boats and casks (barrels)
Danish: Det regner skomagerdrenge / it’s raining shoemakers’ apprentices
Irish (Gaelic): Tá sé ag caitheamh sceana gréasaí / it’s throwing cobblers knives
Norwegian: Det regner trollkjerringer / it’s raining female trolls
Estonian: Sajab nagu oavarrest / it’s raining like from a beanstalk
In any case, I just wish it would!
More at Omniglot: http://www.omniglot.com/language/idioms/rain.php