Issue reported at Wikipédia:Demande d'intervention sur un message système#MediaWiki:Nstab-project – modification de l'interface:
On French wikipedia, for pages of the Projet: (i.e. Project) namespace, "Page" and "Talk" tabs use strange messages for their text contents, namely nstab-projet and nstab-projet_talk, instead of the regular nstab-project and nstab-project_talk.
Demo: https://fr.wikipedia.org/wiki/Projet:Nucl%C3%A9aire?uselang=qqx
This might be set up in the wiki configuration. Could these configuration items please be reset to the standard values?