I solve the problem Unknown option 'francais' by installing the missing language package:
sudo apt-get install texlive-lang-european
Now, encounter the problem Unknown language 'french', the detailed error info is as follows:
! Package babel Error: Unknown language `french'. Either you have
(babel) misspelled its name, it has not been installed,
(babel) or you requested it in a previous run. Fix its name,
(babel) install it or just rerun the file, respectively.
texlive-lang-french is already the newest version.while runningsudo apt-get install texlive-lang-french. – SparkAndShine Jul 07 '15 at 12:50TeX 3.1415926 (TeX Live 2013/Debian). My setting is:./preamble/preamble.tex:\usepackage[francais]{babel}. – SparkAndShine Jul 07 '15 at 13:05\usepackage[french]{babel}? If it works, there's no difference with specifyingfrancais. If it doesn't, then there's something wrong with your installation. – egreg Jul 07 '15 at 13:19