Please install the extension NewUserMessage on French Wikipedia.
Configuration of global variables:
$wgNewUserSupressRC = true;
$wgNewUserMinorEdit = false;
$wgNewUserMessageOnAutoCreate = false;
Welcome message: https://fr.wikipedia.org/wiki/Mod%C3%A8le:Bienvenue_nouveau/automatique (MediaWiki:Newusermessage-template is already pointing to it).
Community consensus: https://fr.wikipedia.org/wiki/Discussion_Projet:Aide_et_accueil#Message_de_bienvenue_via_NewUserMessage