I installed the extension on MediaWiki 1.31 which seems to work fine so far. I just have a problem setting up the available languages. Setting the $mgAvailableLanguage as documented in the LocalSettings.php didn't help and I also can't find the MultiLanguageManager_setup.php.
Might this be an issue with MediaWiki 1.31, or is it just my ignorance? I'm new to MediaWiki.