Please document the feature created in {T69223} and {T153209} (et al).
I tried searching mw, but could not find anything (except for confusing similarly-named functions).
Suggested aspects:
[] Create a section in the Extension:Translate help pages (user and developer)
[] Disambiguate the mention of the magic word {{PAGELANGUAGE}} at https://www.mediawiki.org/wiki/Help:Magic_words#Technical_metadata
[] Disambiguate the older unrelated extension https://www.mediawiki.org/wiki/Extension:PageLanguage
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The item in [[https://meta.wikimedia.org/wiki/Tech/News/2016/51|Tech/News]] that led me here, read:
> Administrators and translation administrators can now use Special:PageLanguage on wikis with the Translate extension. This means you can say what language a page is in. The Translate extension will use that language as the source language when you translate. Previously this was always the wiki's default language. This was usually English. [1]