\makeatletter
+\usepackage{hyphenat}
%
% Customize the titlepage: remove the date, place the publisher name, and
% load a specific file for the verso page, containing some legal notices
}{}
\usepackage{titlesec}
-\titleformat{\chapter}{\huge}{\chaptertitlename\ \thechapter}{20pt}{\Huge}
+\titleformat{\chapter}{\huge}{\thechapter.}{20pt}{\hyphenpenalty=10000 \Huge}
\titleformat{\section}{\Large}{\thesection}{1em}{}
\titleformat{\subsection}{\large}{\thesubsection}{1em}{}
%% \titleformat{\paragraph}{\normalsize}{\theparagraph}{1em}{}