This has been noticed here on the French WP Village Pump: the template {{ de icon}} inside a ref tag (which is a wrong use of this specific template, but this would probably be the same with any template adding a category) adds a [[Category:Articles with German-language external links]] which is left untranslated in the frwiki translation of the enwiki article, instead of the usual way of translating categories.
Topic on Talk:Content translation
Bonsoir, l'outil subst le modèle source quelques fois, il semblerait que ce soit lorsqu'il ne trouve pas de modèle correspondant dans Wikidata. Sur fr.wp, mon bot Framabot supprime les [[Category: afin d'éviter d'avoir des catégories rouges. Mais il ne peut pas supprimer le reste... :(
Sometimes CX seams subst templates, and adds untranslated and not adapted categories. My bot delete it on frwiki, but it would be difficult to detect what is the bad wikicode to suppress entirely the template.
It remember me phab:T144410.