$request: $wgRequest
$mediaWiki: The $mediawiki object
+'MediaWikiServices': Override services in the default MediaWikiServices instance.
+Extensions may use this to define, replace, or wrap existing services.
+However, the preferred way to define a new service is the $wgServiceWiringFiles array.
+$services: MediaWikiServices
+
'MessageCache::get': When fetching a message. Can be used to override the key
for customisations. Given and returned message key must be in special format:
1) first letter must be in lower case according to the content language.