Manual:$wgParserEnableUserLanguage

Statistics and content analysis: $wgParserEnableUserLanguage
Set this to true to allow the {{USERLANGUAGE}} magic word to return the actual user language.
Introduced in version:1.43.0 (Gerrit change 508295; git #10ab0e40)
Removed in version:Still in use
Allowed values:Unspecified
Default value:false

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Set this to true to allow the {{USERLANGUAGE}} magic word to return the actual user language. If it is false, {{USERLANGUAGE}} will return the page language. Setting this to true is discouraged since the page language should typically be used in the content area. Accessing the user language using this feature reduces the efficiency of the parser cache.