Catalan:

Enfilar-se per les parets — To be climbing the walls — To be very angry and / or nervous.

Ficar-se de peus a la galleda — To get one's feet in the bucket — To say or do something inconvenient and / or embarrassing.

N'hi ha per llogar-hi cadires — [Roughly translated] You could rent chairs for this — Refers to something very noteworthy or interesting.

(Anar a) canviar l'aigua de les olives — To (go) change the olives' water — To (leave for a quick) piss.

Descobrir la sopa d'all — To discover garlic soup — To believe you've discovered or come up with something that's commonly known (except, apparently, to you).

(Estar) tocat del bolet — (To be, or have been) touched/hit on the mushroom — (To be) insane.

Fer figa — To do or make fig (literally, the fruit, or figuratively, the vulva) — To become weaker, unable to perform one's intended function.

Fer el préssec — To do or make the peach — To put yourself in a ridiculous situation.

Fer uns ulls com unes taronges — To open one's eyes like oranges — To look very surprised or interested.

Fer pinya — To make (like a) pinecone — To work together for a common cause.

Partir peres — To split up pears — To break up a relationship (sentimental, professional, or otherwise).

Remenar les cireres — To mix up the cherries — To be the person who makes the decisions, to be in control (in a partnership, organisation...). Also, Tallar el bacallà — To cut up the cod. Also, Tenir la paella pel mànec — To hold the pan by the handle.

Somiar truites — To dream of omelettes — To believe things that will hardly be possible to be possible. And, by extension, Somiatruites — Omelette dreamer — Someone who regularly does that; an extremely unreasonable optimist.

Suar la cansalada — To sweat (the) bacon — To do very hard tiring work or exercise.

Aixecar la camisa — To lift (someone's) shirt — To scam, misdirect, or lie (to someone).

Això són figues d'un altre paner — These are figs from a different container — This is a completely different matter (than what we were talking about).

Bon vent i barca nova! — Good wind and a new boat! — Farewell to someone or something you'd rather never see again.

(Això és) bufar i fer ampolles — (This is) (like) blowing and making bottles — Refers to something that's very easy to do or achieve. Can be used literally or ironically.

Caure-hi de quatre potes / peus — To fall in with all four legs / feet — To fall for a scam or lie.

(Ser) cornut i pagar el beure — (To be a) cuckold (literally, to have horns) and pay for the drinks — To voluntarily sacrifice for others who take advantage of you.

(Donar) gat per llebre — (To give) a cat pretending it's a hare — To lie, scam, or misdirect. To substitute a lower quality product for what you agreed to provide.

El més calent és a l'aigüera — The hottest stuff is in the sink — Work hasn't even started yet on whatever endeavour we're talking about.

En un tres i no res — In a three and nought — In a very short time.

La mare dels ous — The mother of the eggs — The main cause or reason (of/for something).

Lligar els gossos amb llonganisses — To tie up the dogs with sausages — To be wealthy.

Fer mans i mànigues — To do/make hands and sleeves — To put as much effort as possible into something.

Fer un riu — To make a river — To piss.

Veure el llautó — To notice the brass — To notice the concealed truth behind appearances. (Literally, it refers to noticing something is made of a poorer quality metal than it's claimed to be.)

Tenir mà esquerra — To have (sic) left hand — To be good at diplomacy.

Un orgue de gats — An organ (musical instrument) made out of cats — A very noisy and chaotic room or place.

And there's plenty more, but I've already spent more time than I could afford typing these.

Oh, but also, not exactly an idiom, maybe, but something I've always thought says a lot about Catalan worldview: the Catalan word for pigsty is cort. Which is exactly the same word (and with the same meaning) as the Catalan word for court. As in royal court.

Maybe that's where Orwell got his idea for Napoleon & co to be pigs..?