Change 483304 had a related patch set uploaded (by MaxSem; owner: MaxSem):
[mediawiki/core@master] Display translatable images in user language on image pages

https://gerrit.wikimedia.org/r/483304

I've implemented what's being currently requested in the above patch, however let's be sure we understand all the details:

• On local wikis, it makes sense to use wiki language
• On Commons, the default language is English - however the whole wiki makes this almost transparent, using user's UI language as fully as possible. Does it make sense to use user language on Commons?

In T210814#4867916, @MaxSem wrote:

I've implemented what's being currently requested in the above patch, however let's be sure we understand all the details:

• On local wikis, it makes sense to use wiki language
• On Commons, the default language is English - however the whole wiki makes this almost transparent, using user's UI language as fully as possible. Does it make sense to use user language on Commons?

There is one possible pitfall of doing that. Commons file page UI does not make it very clear when you are viewing a file in a given language versus when you are viewing a file that has been switch translated into a given language. If we start to show images by default in user's language, we might make that problem worse by tricking people into thinking that the file is only available for the language they see it in. They might go ahead and embed it in wikis where that's not the default language (maybe a variant/closely related language) and the file will end up with English labels on that wiki.
Hence, I think it's best if we let the default language for files on Commons remain English.

Hmm, makes sense. Final question: do we need a flag for it, and if yes, should $wgMediaInTargetLanguage suffice? I was actually thinking of deprecating it as the original feature it was added for works fine enough to just be always on. Ping @Mooeypoo, @Samwilson and @MusikAnimal.

We could keep the same flag and deprecate it after a while once we know it doesn't cause anything to blow up.

I don't think this needs a feature flag (and I agree, @MaxSem, that wgMediaInTargetLanguage should be deprecated). The above patch looks good to me.

Poke. This ticket has been sitting for a while.

I don't think we have a consensus re configuration variable?

In T210814#4926077, @MaxSem wrote:

I don't think we have a consensus re configuration variable?

It's up to you if you want to keep it or not.

OK, I'll side with Sam then and not use it.

And in such case, this change is ready for review.

Change 483304 merged by jenkins-bot:
[mediawiki/core@master] Display translatable images in wiki language on image pages

https://gerrit.wikimedia.org/r/483304

This has been deployed. I tested with https://de.wikipedia.org/wiki/Datei:Equatorial_coordinates.svg and it works as expected. I couldn't find other test files to try with.