Of course the French have some slang words and expressions borrowed from English or translating the English: tu parles (you said it) or avior deux cordes a son arc (to have two strings to one's bow). But really to know a language is to be able to come up with the appropriate word - and that may not be the one they taught you in school.
Ashley, Leonard R. N.
"Calling A Cat A Cat,"
Word Ways: Vol. 24
, Article 18.
Available at: http://digitalcommons.butler.edu/wordways/vol24/iss1/18