It looks like that language string isn't filled out for your language. Please edit the /language/fr_FR/fr_FR.mod_sclogin.ini file. At the bottom, add the following line:
MOD_SCLOGIN_SOCIAL_INTRO_TEXT_LABEL="Or login with your social network credentials"
That string on the right can be whatever you want to display, or it can be two double-quotes "" if you don't want anything to appear there.
I hope that helps get you going,
Alex
Sentence above the social buttons
