Steps to reproduce:
1. Start the portal with properties:
Or just start with default properties and once logged in, change your user language to French, in My Account or with the Language Selector portlet.
2. Place a Calendar portlet on a page and switch to Day view (Jour).
In the header, you can see the date appearing as (see attached screenshot):
Mercredi, Janvier 11, 201
But the date format usually used in France should look like:
Mercredi 11 Janvier 2017
This Wikipedia article (https://en.wikipedia.org/wiki/Date_and_time_notation_in_France) seems to confirm this claim.