$l10nCache = Language::getLocalisationCache();
$messageNames = $l10nCache->getSubitemList( 'en', 'messages' );
// Normalise message names for NS_MEDIAWIKI page_title
$l10nCache = Language::getLocalisationCache();
$messageNames = $l10nCache->getSubitemList( 'en', 'messages' );
// Normalise message names for NS_MEDIAWIKI page_title