The MobileFrontend's search functionality displays the mobile-frontend-search-content-no-results message (currently set to '''{{int:mobile-frontend-search-content}}''' to see if this phrase appears anywhere.), using an embedded {{int:mobile-frontend-search-content}} to insert a bolded Search within pages phrase.

However, the construction (together with the message definition) causes the embedded {{int:}} to use the content language of the wiki instead of the user's UI language like the rest of the message. That means the users sees a bilingual mixed message whenever she uses a different UI language than the wiki content language.

For instance: go to https://cs.m.wikipedia.org/wiki/X?uselang=en and write some nonsense to the search box. You'll get "No page with this title. Hledat v obsahu stránek to see if this phrase appears anywhere." with a Czech translation of the subphrase within the English message. (Or vice versa: go to https://en.m.wikipedia.org/wiki/X?uselang=cs and write some nonsense there, and you'll get "Neexistuje žádná stránka s tímto názvem. Search within pages, zda se tento text někde neobjevuje.")

This bug have probably been reported already at T74985, which is now Closed, Invalid. Not sure if something changed since then or not, but this is definitely a bug, so the resolution does not make much sense to me.

Developer notes

Some screenshots illustrate the problem: