I was given a book by Charles Timony called Pardon My French by my wife for my birthday.
It is a dream of a book for a language nerd like me.

The author loves pointing out those huge moments when the dictionaries let us down, in fact exactly when we become lost in translation.

I have picked out a few of his plums and will probably give you some more in the future.

When I was stopped by a large family group in Collioure a few years ago and asked to photograph the whole family together I rather nastily said “Dits Fromage” at them which they all dutifully did, their mystification evident on their faces.
What I should of course have said was “Dits Ouistiti”which is how the French make themselves smile. In a similar vein the true Coq, as against the Cock, says Cocorio instead of Cock a Doodle Doo.

There are a couple of instances where our French dictionaries in school positively let us down. Un Tapis, is not really a carpet but a rug, Moquette is in fact the word for what we call carpet, Velo is the word for bicycle much more so than bicyclette which they told us was the word in school.
Another one worth remembering , especially if it is your tipple, is never order Scotch in a pub or Café. If you do will be given a roll of sellotape.