Wikimedia Bugzilla is closed!

$wgNamespacesWithSubpages = 
      array( -1 => 0, 0 => 0, 1 => 1, 2 => 1, 3 => 1,
             4 => 0, 5 => 1, 6 => 0, 7 => 1, 
             8 => 0, 9 => 1, 10 => 0,11 => 1,
             100 => 1, 101 => 1 );

or add in LocalSettings.php:

$wgNamespacesWithSubpages = array(
        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
);