My doctor is from Montenegro. Recently while getting a checkup, he noticed that I had a very subtle, benign heart murmur. After listening to me express concern, he went out of his way to make sure I was comfortable and knew I had nothing to fret about.
“Why, just look how healthy you are, what shape you’re in. Look at your body. You could pull the ox’s tail!”
AFAIK, in Mexico ‘codo’ means “elbow” and used to refer to people who are cheap. The usage I’ve seen is when a person is being a stingy, another person would tap their elbow and give a knowing look.
Good-natured Hungarian toast:
“Baszom a szád szélét, Sanyikám!”
“I fuck the corner of your mouth, my dear Alexander!”
I dunno if that’s strictly an idiom, actually, but you can tell I’ve been wanting to share it for some time.
There are a lot of these in Finnish that are really great to hurl around when mad but lose their brevity and effectivity in translation. For example, the phrase “kyrpä otsassa” means “cock on your forehead”. When something annoying or irritating is happening for a lengthy period of time and you get increasingly annoyed and pissed off by it, you say you are growing a cock on your forehead. A slightly censored version of this expression is “tatti otsassa”, tatti being a boletus mushroom, which somewhat resembles a penis.
Now imagine going through the above explanation with a foreign-exchange student who recognized the word “tatti” and wanted to know why we were talking about mushrooms. It was not a very enlightening conversation apparently.
Another one which I love is “pilkunviilaaja”, which means someone who files away at a comma. This means a person who is overly nitpicky over details. A more crude version is “pilkunnussija”, comma-fucker.
In Norwegian, if something is really ugly, effed up or shoddily made in some way, it “does not look like the pig”.
Not just “a”, but “the” pig. I have no idea which pig is being referred to.
And strangely enough, saying that something does look like the pig is not a compliment, although it logically should be.
Pigs is cute!
And if you say they’re not, I’ll burn down your fish pond! (Czech insult.)
Some good ones:
enculer des mouches: to pick nits. literally, “to sodomize flies.”
accouche qu’on baptise!: Get on with it! or Spit it out! literally, “give birth so that we can baptize!” Often shortened to Accouche!
coiffer sainte Catherine: of a young woman, not to be married yet (with the implication that time is of the essence). Literally, “to give a hat to Saint Catherine”: in certain places, the church had a statue of Saint Catherine that was furnished with a new hat every year, and changing the hat was the privilege of unmarried women over 25.
esprit de bottine: simple-minded reasoning; literally, “the mind of an ankle-boot.”
peter plus haut que son cul: to be stuck-up; literally, “to fart higher than one’s ass.”
avoir le front tout le tour de la tête: to be audacious/impertinent/arrogant/chutzpah, to have gall/effrontery/some nerve; literally, “to have a forehead that goes all the way around one’s head.”
brasse-Canayen: turbulence, frantic activity: literally, “[French]-Canadian-shaking.”
s’habiller comme la chienne à Jacques: to be dreadfully dressed; literally, “to be dressed like James’s bitch” (although whether in the sense of “female dog” or another sense, I do not know).
And a very creepy one:
faiseuse d’anges: a woman who provided illicit abortions, or (in even further bygone days) “disposed” of unwanted infants. Literally, “angel-maker.”
Two Spanish ESL teachers wrote a book consisting completely of direct translations from Spanish into English; it was so succesful that they did a follow-up. I do wish they had bothered add actual translations to the list of literal ones, though!
The books are called Speaking in Silver (hablando en plata; “calling a spade a spade”) and From Lost to the River (de perdidos al río; “from the frying pan into the fire”).
Spanish has a sentence similar to that coiffer sainte Catherine: an unmarried woman who’s over marriageable age is said to be “dressing saints”, se ha quedado para vestir santos. Another expression is se le ha pasado el arroz, “her rice has been cooking for too long.”
In Swedish, that same woman would be described as hon sitter på glasberget, “she’s sitting on the glass mountain.”
Some other expressions: **
stå med skägget i brevlådan**, to be stumped or have one’s plans dashed. Literally to “stand with your beard (caught) in the mailbox”.
få arslet ur vagnen, to get your shit together: “to get your ass out of the pram”. Another common phrase with the same meaning is få tummen ur röven, “to get your thumb out of your ass”.
ha tomtar på loftet, “to have gnomes in your hay loft”. In other words, bats in the belfry.
du ska få dina fiskar varma “you’re going to get your fish warm” - you’re in trouble!
nu är det kokta fläsket stekt: “now the boiled pork has been fried” - we’re in trouble!
nu har han satt sin sista potatis: “now he’s planted his last potato” - he’s done for.
The most common insult in Czech is “do prdele,” which roughly translates to “go to an ass.”
And this is why, after four years of (A+) high-school French, I barely have a clue what you guys are talking about. 
I heard it as “péter plus haut que le trou”, actually.
The OP said idioms that dont translate, but I’m totally stealing the English translation of this. 
I’ve always been amused by the fact that “bragging” in Chinese (“吹牛”) literally means “blowing the cow.” I’d like to hear the story behind that one.
German:
Mach’ nicht so ein Theater= don’t make drama, or as my sister freely translated: Don’t turn it into a three-act opera. I use this daily!
Another German:
Du hast nicht alle Tassen im Schrank - You don’t have all the cups in the cupboard, meaning: You are crazy. Don’t know where it comes from.
Norwegian: Hun har ben i nesen - She is strong-willed, she doesn’t give up easily, she’s a fighter - but literally, she has bone in the nose! It seems to be used about women much more than about men, and it is intended as a compliment.
Ha! Swedish has the same idiom in hon har skinn på näsan - she has skin on her nose.
Makes you wonder whether noses with skin and bone were outside the norm with our common ancestors. :eek:
The journal Maledicta apparently ran an article many years ago about cursing in some island (I can’t recall which – I think it was in Southeast Asia), in which “You’re Lying!” was given in idiomatic form as “Your asshole is full of blue mud!”. It’s not all that different from the english equivalent “You’re full of shit!”, but more picturesquely expressed.