When babel creates a new user category using MediaWiki:Babel-autocreate-text-levels and MediaWiki:Babel-autocreate-text-main, it interprets the content of the page. It means that if a template is used for these categories (as on WP:FR), we cannot make babel generate the pages with the template as this one is transcluded. We tried on WP:FR (see [[//fr.wikipedia.org/w/index.php?title=MediaWiki:Babel-autocreate-text-levels&action=edit|this message]]) to use the template, and got [[//fr.wikipedia.org/w/index.php?title=Cat%C3%A9gorie:Utilisateur_dar-0&action=edit&oldid=153921442|this behavior]] instead of [[//fr.wikipedia.org/w/index.php?title=Cat%C3%A9gorie:Utilisateur_dar-0&action=edit|that one]].
As suggested by an administrator on [[//fr.wikipedia.org/wiki/Wikip%C3%A9dia:Demande_d%27intervention_sur_un_message_syst%C3%A8me#MediaWiki:Babel-autocreate-text-levels_et_MediaWiki:Babel-autocreate-text-main_–_Contenu_par_défaut_des_pages_créées_par_babel_autocreate|this page]], this has to do with the function **BabelAutoCreate::create()**, which should use **->plain()** instead of **->text()**.
I'm not familiar with the WM extensions code, so I wouldn't know if this is the correct action to take. However, using templates is a basic action of wikipedia, and babel should support it.
I found the T168610 task in which the same issue is reported.
Thanks, Epok.