Omar,
The Login with Facebook text should definitely be in the com_jfbconnect.ini file using the COM_JFBCONNECT_LOGIN_USING_FACEBOOK string. If that's not working, can you try updating that in the English language file to see if for some reason it's being read from there? If so, are you using any 3rd party language switchers or something else not part of Joomla for your multi-lingual support?
For the SCLogin modules strings, those are in the mod_sclogin.ini file. Copy those to es_ES and translate as well.
As always, if you're having issues, just let us know and we can look into it further!
Thanks,
Alex