I translate FR messages for new created pages. Althtough the messages are correcly saved, even after a purge action, the FR option still does not appear in the bar of languages.
Page:
https://www.mediawiki.org/wiki/Manual:$wgMessagesDirs
Exist:
https://www.mediawiki.org/w/index.php?title=Translations:Manual:$wgMessagesDirs/Page_display_title/fr&action=edit
bar:
Autres langues :
English · dansk · español · magyar · polski · русский · 日本語
True also for other pages: https://www.mediawiki.org/wiki/Manual:GenerateJsonI18n.php