Well there's always the {{int:.. hack. Harder to pretend like it doesn't exist if we use it on a developer wiki.

I implemented $wgTranslatePageTranslationULS a while ago. It does what the summary says, but that's probably not what you want: it does not automatically serve the content in the interface language, just when changing languages. Special:MyLanguage complements it.

(In reply to Bawolff (Brian Wolff) from comment #1)

Well there's always the {{int:.. hack. Harder to pretend like it doesn't
exist if we use it on a developer wiki.

This bug is about the effects of language selection itself, not about in-page links or transclusion. For that we have bug 2085 (based on user language, to replace the int:Lang hack, mainly for transclusion) and bug 57603 (to keep content language constant) as well as bug 45096 (which is about transclusion but didn't define if constant by user language or content language).

(In reply to Niklas Laxström from comment #2)

I implemented $wgTranslatePageTranslationULS a while ago. It does what the
summary says, but that's probably not what you want: it does not
automatically serve the content in the interface language, just when
changing languages. Special:MyLanguage complements it.

I've updated docs a bit.
https://www.mediawiki.org/wiki/Extension:UniversalLanguageSelector#Page_translation
https://www.mediawiki.org/wiki/Help:Extension:Translate/Configuration#Page_translation_feature
https://www.mediawiki.org/wiki/MyLanguage

Sorry if I wasn't clear. The use case is this:

Russian speaker lands in http://mediawiki.org

Hopefully she will get the content in Russian thanks to browser language detection, but if she gets it in English:

EXPECTED

If the interface and content is in English, the user selects "Russian", and then both interface and content are shown in Russian, https://www.mediawiki.org/wiki/MediaWiki/ru?setlang=ru

ACTUALLY

After the user selects Russian, the interface changes to Russian, but the content stays in English, https://www.mediawiki.org/wiki/MediaWiki?setlang=ru

Usually websites have a single language selector for everything, not a language selector at the top for the UI, and then a big box with languages to select the content.

(In reply to Quim Gil from comment #5)
As far as I can see, this has been implemented in Translate.

Not this bug and no bug needed, but I've submitted https://gerrit.wikimedia.org/r/#/c/115879/ for mediawiki.org per comment 5. It won't eliminate the need for <languages/> at the top of the main page, to be clear.

I know it's me and I really mean it: I don't understand how this bug is fixed but then as registered user I can't get mediawiki.org to behave as described in comment #5. But I trust you and I'm happy to see that you do understand the problem. Thank you for the patch, a step in the good direction.

It's the usual distinction fixed in master vs. deployed on your wiki vs. actually *enabled* on said wiki.