Comment # 34 on bug 904524 from Wolfgang Bauer

(In reply to Wolfgang Bauer from comment #33)
> Or are those translations in desktop-translations?

To answer myself here: yes, they are.
But they would probably be in there also if /usr/share/wallpapers/ is not
stripped IIUIC. So not really a reason to have it in the list, is it?

Btw, I just noticed that also some other wallpapers are not translated here
(13.2/KDE4) even though the translations are available in the .desktop files
themselves.
It seems that KDE (4 and 5) just doesn't support to have an xxx.png.desktop
file for a wallpaper xxx.png, it apparently wants a metadata.desktop.

As a side-note: I just tried in GNOME, and that doesn't show a name at all for
wallpapers...