In English, 'preservatives' are substances that we use to stop products decaying. For example, a manufactured drink or food product may contain preservatives so that it lasts longer and you don't need to keep it in the fridge.
In French, 'préservatifs' are condoms. Could be embarrassing.
sympathetic / sympathique
- sympathique en Francais = pleasant, friendly
exhibition in English = exposition en Francais
- exhibition en Francais = flashing as in indecent exposure of your naked body
Here are a few false friends I could think of:
1. to pretend = faire semblant
prétendre = to claim
2. a coin = une pièce
un coin = a corner
3. pain = douleur
pain = bread
4. a library = une bibliothèque
une librairie = a book shop
5. to pass an exam = réussir un examen
passer un examen = to take an exam
6. a hazard = un danger
le hasard = chance
7. a physician = un médecin
un physicien = a physicist
8. actually = en fait
actuellement = currently
french : Actuallement = currently
english : Actually = in fact
The English word "sensible" is a false friend for all Romance language native speakers, including the French. In English, it means having good sense, reasonable, practical. In French, "sensible" = sensitive, which has a different meaning in English.
I think "sensible" also meant sensitive in English in the past, and this meaning lives on in the noun "sensibility", which readers of Jane Austen will be familiar with.