The problem is that until now the ~2 package is not the one selected in the jessie-backports repo.
administrateur@pccorei7-4770:~$ apt-cache policy libreoffice-l10n-fr
libreoffice-l10n-fr:
Installé : 1:5.0.1-1~bpo8+2
Candidat : 1:5.0.1-1~bpo8+2
Table de version :
*** 1:5.0.1-1~bpo8+2 0
100 /var/lib/dpkg/status
1:5.0.1-1~bpo8+1 0
1:4.3.3-2+deb8u1 0
Could you please fix this ? This would avoid many mails to you.