Something

$wgNamespacesWithSubpages = array(
        NS_MAIN           => true,
        NS_TALK           => true,
        NS_USER           => true,
        NS_USER_TALK      => true,
        NS_PROJECT_TALK   => true,
        NS_IMAGE_TALK     => true,
        NS_MEDIAWIKI_TALK => true,
        NS_TEMPLATE_TALK  => true,
        NS_HELP_TALK      => true,
        NS_CATEGORY_TALK  => true,
        100               => true,
        101               => true
);