Manual:$wgExtraGenderNamespaces

Details
Same as $wgExtraNamespaces, but for namespaces with gender distinction (user space). You have to define this by yourself if you have extra namespaces which need gender distinction.

the default form for the namespace should also be set using $wgExtraNamespaces for the same index.

Example: In this example the namespace name fallbacks to the MediaWiki default, so nothing needs to be added to.

In case the language of the wiki as set with the $wgLanguageCode parameter has a native distinction of gender the change of the namespace's name will be done automatically for the ones provided natively by MediaWiki. In case you would like to prevent this from happening, you will have to override this by setting this parameter explicitly not to do this, e. g. for German:

Usually the female version of user would correctly be "Benutzerin" in German.