I love this stuff.
Over hereIn France they say 'chouette' when something's cool. Sorta like sweet. But une chouette is an owl. So basically they're all walking around going "owly"/"That's WELL owl". Nathan Barley or what.
Another good one is "mets la puce a l'oreille" which means to give you an idea or to put the thought in your mind. Literally translates as "to hold the flea up to you ear". Similarly, when pigs fly / when hell freezes over is "quand les poules auront les dents" which means when the chickens have teeth. However, the best version of that I got from sister, who's a russian student. Apparently their version translates as "When the crayfish on the hill whistles". Which is just amazing.
Gimme more literal translations of foreign language idioms what you know etc.