Translations for french language have a lot of mistakes
Problems are visible of course in the PO file:
https://gitlab.com/gitlab-org/gitlab-ce/blob/master/locale/fr/gitlab.po
For example line 108, participants is translated by "participant·e·s".
This is not standard french, the correct translation is "participants".
The "·" sign doesn't exist in French.
I can help you fix that if you want.