These "Did you know..." subpages are randomly displayed using {{ Random portal component}}.
This rather slow Toolserver query returns a list of talk pages that have been tagged by WikiProject France and have the standard box describing a DYK appearance.
The portal used to display a single page, Portal:France/Did you know, which was updated from time to time. The archive page Portal:France/Did you know archive is a record of the selections made there.