The most fashionable these days : petit pot de creme (yes the names of my blogs are jokes) . Translation in French is little cream jar. Which could be anything dairy in a small container in France, from a pot of sour cream to a little jar of milk, or a delicacy cooked in the oven. In American it's a custard dessert cooked in the oven. Custard in French is known as Creme Anglaise (English cream). It's a common dessert in France, but since I read a famous American cook giving a recipe of petit pot de creme with half and half, it's not a French thing anymore. Half and half is not sold in France, and if so, would be considered unhealthy if not gross.
Decolletage: the French translation would be decolleté. Decolletage is not a French word. Don't try it over there, it sounds as weird as douche (shower in French) here.
French manicure: not really a French word, I know. But if you ever go to France and need a French Manicure, ask for a Californian Manicure. I wonder who had the idea first?
Entrée: in French, entrée is the word for appetizer. Entrée translates by main course. Don't ask me to translate appetizer, since apéritif is the drink and snack you nibble on before lunch or dinner. Happy hour doesn't exist in France, or I would really get lost in translation. Translating the menu for French tourists is a torture.
Café au lait: as you probably know if you buy coffee in cardboard cups, café au lait is a mix of regular coffee and hot milk. Interestingly enough, regular coffee is not sold in France (see half and half). Café au lait, in France, is an expresso with hot steamed milk (and little foam). So a café au lait in France is really a latte. In Italy, latte means milk. Anyway, if you end up in a French cafe, craving for a latte, ask for a "grand creme" (big cream). Which brings us back to the petit pot de creme, but no cooked custard is involved.
Anyway , no big deal. It's in the nature of a language to use foreign words to extend to necessary new words. If you ever need sneakers in Paris, look for baskets.
Je peux pas traduire, je vais mourir de la tete la. Sachez juste que si vous croisez un mot Francais en Americain, fuyez. Vite, de la confiture de groseilles!