Index: src/wp-admin/includes/class-wp-upgrader.php
===================================================================
--- src/wp-admin/includes/class-wp-upgrader.php	(revision 30373)
+++ src/wp-admin/includes/class-wp-upgrader.php	(working copy)
@@ -1370,9 +1370,7 @@
 		remove_filter( 'upgrader_source_selection', array( $this, 'check_package' ) );
 
 		if ( $parsed_args['clear_update_cache'] ) {
-			wp_clean_themes_cache( true );
-			wp_clean_plugins_cache( true );
-			delete_site_transient( 'update_core' );
+			_clear_update_transients();
 		}
 
 		return $results;
@@ -2200,9 +2198,7 @@
 			}
 
 			// Clear existing caches
-			wp_clean_plugins_cache();
-			wp_clean_themes_cache();
-			delete_site_transient( 'update_core' );
+			_clear_update_transients();
 
 			wp_version_check();  // check for Core updates
 			wp_update_themes();  // Check for Theme updates
Index: src/wp-includes/update.php
===================================================================
--- src/wp-includes/update.php	(revision 30373)
+++ src/wp-includes/update.php	(working copy)
@@ -648,6 +648,17 @@
 	}
 }
 
+/**
+ * Clear existing update caches for plugins, themes, and core.
+ *
+ * @since 4.1.0
+ */
+function _clear_update_transients() {
+	wp_clean_plugins_cache();
+	wp_clean_themes_cache();
+	delete_site_transient( 'update_core' );
+}
+
 if ( ( ! is_main_site() && ! is_network_admin() ) || ( defined( 'DOING_AJAX' ) && DOING_AJAX ) )
 	return;
 
@@ -669,6 +680,8 @@
 add_action( 'wp_update_themes', 'wp_update_themes' );
 add_action( 'upgrader_process_complete', 'wp_update_themes', 10, 0 );
 
+add_action( 'update_option_WPLANG', '_clear_update_transients' , 10, 0 );
+
 add_action( 'wp_maybe_auto_update', 'wp_maybe_auto_update' );
 
 add_action('init', 'wp_schedule_update_checks');