Thank you, @Nike:. Do you know on which pages these messages are used?
Guycn2 · ☎
@Guycn2: They are used on file description pages for video and audio files under the heading "⧼timedmedia-status-header⧽". See e.g. this video on Commons.
Jon Harald Søby (talk)
Thanks a lot. It seems that PLURAL actually does work on these messages.