See https://commons.wikimedia.org/wiki/Foo for example:
This entity does not exist. You can search the related logs to find out where it went.
This should be using the default message for this purpose, which is about a regular wiki page, not a Wikidata entity.
This is likely due to technical debt in the WikibaseRepo.
Could you link the page its showing that on? When I try to reproduce it I don't see any message like that.
It's on the address in the task description for me, but that might be different for you given that "Foo" is no longer a normally non-existent gallery, it is now a formerly-existant gallery (someone created it, someone deleted it).
Try anything like https://commons.wikimedia.org/wiki/Somethingnonexistent.
EDIT: It seems to be different depending on whether the user is logged-in. For me in private browsing mode it correctly says "This page". When logged-in, it says "This entity".
Strange!
Weird, I went to your link in both incognito and normal (I was logged in with normal) and both times it said "This page". (also apparently phab decided to format your message)
The bug is currently obscured on Wikimedia Commons. It looks like someone has overidden the "This entity" message for English to say "This page" instead.
My interface langauge is en-gb, which the community has not worked around for yet.
Try https://commons.wikimedia.org/wiki/Somethingnonexistent?uselang=en-gb to see the problem again. And this shows it for logged-out users as well.
(Thanks! I've reported the Phabricator bug.)
ah yeah, if I use that then I see it saying "This entity" both in normal (logged in) browsing and in incognito browsing