If I understand correctly you are only looking for "2012". If that is so, then there is no need for regex, just a simple search and replace. Try:
Replace: Janv. 2012
if you are looking for ANY year then you can try this Regex:
Replace: Janv. \1
I'm not sure what flavor of regex Calibre uses. You may have better luck if you check in their forum. This one is for the Sigil software.
Last edited by Turtle91; 01-06-2013 at 08:58 AM.