Spotted in production:
Catchable fatal error: Argument 2 passed to PageTranslationHooks::onPageContentLanguage() must be an instance of Language, StubUserLang given in /srv/mediawiki/php-1.31.0-wmf.2/includes/Hooks.php on line 177
Mostly trying to remove stubbing entirely, but there might need to be a quicker bandaid fix for this.