We translators come across a lot of them.
mettre en valeur: This means sort of to show something off to its best advantage, or to arrange it and its surroundings to give it pride of place, or to do something to make it more profitable. As in On a transféré La Joute de Riopelle au centre-ville afin de le mettre en valeur (Riopelle’s sculpture La Joute was moved downtown, where it could be set up in such a way as to show it off to its best advantage.)
aménagement: Design or layout of an area, especially an open space, to serve some function. Un terminus d’autobus sera aménagé aux abords de la station Côte-Vertu (The area surrounding Côte-Vertu station will be set up as/built into a bus terminus). An open space or the interior of a building could be aménagé for some purpose. Related is réaménager (to alter or rearrange some area, interior, etc., to change its function.)
faire en sorte: to permit/cause it to happen that… Le réaménagement des voitures du métro fera en sorte que plus de passagers puissent y entrer (rearranging the metro cars will allow more passengers to enter). Not so much an untranslatable idea as an untranslatable construction.
animateur: someone who runs any kind of a meeting or event and makes people be interested and do stuff. It could be a facilitator, presenter, or emcee. More and more, we’re breaking down and just saying “animator” for it.
stage: an internship, locum, apprenticeship., or even a work-study project or workplace visit. Basically, the opportunity to enter a workplace as a sort of temporary sub-employee. Paid or unpaid. We say this in Quebec English a lot (“I did a stage at the STM”), pronounced as in French (“stahzh”).
vernissage: literally “varnishing,” but it means a party that someone throws at which they show off their art. It can, but isn’t necessarily, a gallery opening. Often used in Quebec English (“we’re going to Bruce’s vernissage tonight”).
cinq à sept: a party, sort of like a cocktail party only classier, between 5 and 7 PM.
niaiseux: irritating, obstreperous, given to foolish or stupid behaviour, naive, whiny, etc. Thirteen-year-old boys are in a state of almost perpetual niaiserie.
Accouche qu’on baptise ! “Give birth so we can baptize!” An extremely impatient way of saying get on with it, there are people waiting for what you’ve been called upon to produce.