Tracking so I know it exists and needs fixing eventually:

[645067280107972222e7827c] /wiki/Special:ManageMessageGroups MediaWiki\Config\ConfigException: $wgCacheDirectory must be configured

Backtrace:

from /var/www/mediawiki/extensions/Translate/src/Utilities/Utilities.php(264)
#0 /var/www/mediawiki/extensions/Translate/src/Synchronization/MessageChangeStorage.php(45): MediaWiki\Extension\Translate\Utilities\Utilities::cacheFile()
#1 /var/www/mediawiki/extensions/Translate/src/Synchronization/ManageGroupsSpecialPage.php(114): MediaWiki\Extension\Translate\Synchronization\MessageChangeStorage::getCdbPath()
#2 /var/www/mediawiki/includes/specialpage/SpecialPage.php(728): MediaWiki\Extension\Translate\Synchronization\ManageGroupsSpecialPage->execute()
#3 /var/www/mediawiki/includes/specialpage/SpecialPageFactory.php(1717): MediaWiki\SpecialPage\SpecialPage->run()
#4 /var/www/mediawiki/includes/actions/ActionEntryPoint.php(504): MediaWiki\SpecialPage\SpecialPageFactory->executePath()
#5 /var/www/mediawiki/includes/actions/ActionEntryPoint.php(146): MediaWiki\Actions\ActionEntryPoint->performRequest()
#6 /var/www/mediawiki/includes/MediaWikiEntryPoint.php(200): MediaWiki\Actions\ActionEntryPoint->execute()
#7 /var/www/mediawiki/index.php(58): MediaWiki\MediaWikiEntryPoint->run()
#8 {main}