Index: src/wp-includes/ms-functions.php
===================================================================
--- src/wp-includes/ms-functions.php	(revision 40509)
+++ src/wp-includes/ms-functions.php	(working copy)
@@ -1138,13 +1138,13 @@
  * @param string $title   The new site's title.
  * @param int    $user_id The user ID of the new site's admin.
  * @param array  $meta    Optional. Used to set initial site options.
- * @param int    $site_id Optional. Only relevant on multi-network installs.
+ * @param int    $network_id Optional. Only relevant on multi-network installs.
  * @return int|WP_Error Returns WP_Error object on failure, int $blog_id on success
  */
-function wpmu_create_blog( $domain, $path, $title, $user_id, $meta = array(), $site_id = 1 ) {
+function wpmu_create_blog( $domain, $path, $title, $user_id, $meta = array(), $network_id = 1 ) {
 	$defaults = array(
 		'public' => 0,
-		'WPLANG' => get_site_option( 'WPLANG' ),
+		'WPLANG' => get_network_option( $network_id, 'WPLANG' ),
 	);
 	$meta = wp_parse_args( $meta, $defaults );
 
@@ -1160,14 +1160,14 @@
 		$path = '/';
 
 	// Check if the domain has been used already. We should return an error message.
-	if ( domain_exists($domain, $path, $site_id) )
+	if ( domain_exists($domain, $path, $network_id) )
 		return new WP_Error( 'blog_taken', __( 'Sorry, that site already exists!' ) );
 
 	if ( ! wp_installing() ) {
 		wp_installing( true );
 	}
 
-	if ( ! $blog_id = insert_blog($domain, $path, $site_id) )
+	if ( ! $blog_id = insert_blog($domain, $path, $network_id) )
 		return new WP_Error('insert_blog', __('Could not create site.'));
 
 	switch_to_blog($blog_id);
@@ -1198,10 +1198,10 @@
 	 * @param int    $user_id User ID.
 	 * @param string $domain  Site domain.
 	 * @param string $path    Site path.
-	 * @param int    $site_id Site ID. Only relevant on multi-network installs.
+	 * @param int    $network_id Network ID. Only relevant on multi-network installs.
 	 * @param array  $meta    Meta data. Used to set initial site options.
 	 */
-	do_action( 'wpmu_new_blog', $blog_id, $user_id, $domain, $path, $site_id, $meta );
+	do_action( 'wpmu_new_blog', $blog_id, $user_id, $domain, $path, $network_id, $meta );
 
 	wp_cache_set( 'last_changed', microtime(), 'sites' );