Index: src/wp-includes/class-wp-customize-widgets.php
===================================================================
--- src/wp-includes/class-wp-customize-widgets.php	(revision 27740)
+++ src/wp-includes/class-wp-customize-widgets.php	(working copy)
@@ -429,7 +429,7 @@
 	 */
 	static function parse_widget_setting_id( $setting_id ) {
 		if ( ! preg_match( '/^(widget_(.+?))(?:\[(\d+)\])?$/', $setting_id, $matches ) ) {
-			return new WP_Error( 'invalid_setting_id', 'Invalid widget setting ID' );
+			return new WP_Error( 'invalid_setting_id', __( 'Invalid widget setting ID.' ) );
 		}
 
 		$id_base = $matches[2];
@@ -923,13 +923,13 @@
 			$sanitized_widget_setting = json_decode( self::get_post_value( 'sanitized_widget_setting' ), true );
 			if ( empty( $sanitized_widget_setting ) ) {
 				$options_transaction->rollback();
-				return new WP_Error( 'malformed_data', 'Malformed sanitized_widget_setting' );
+				return new WP_Error( 'malformed_widget_setting', __( 'Malformed widget setting.' ) );
 			}
 
 			$instance = self::sanitize_widget_instance( $sanitized_widget_setting );
 			if ( is_null( $instance ) ) {
 				$options_transaction->rollback();
-				return new WP_Error( 'unsanitary_data', 'Unsanitary sanitized_widget_setting' );
+				return new WP_Error( 'unsanitary_widget_setting', __( 'Unsanitary widget setting.' ) );
 			}
 
 			if ( ! is_null( $parsed_id['number'] ) ) {
@@ -970,13 +970,14 @@
 		if ( 0 !== $options_transaction->count() ) {
 			if ( count( $options_transaction->options ) > 1 ) {
 				$options_transaction->rollback();
-				return new WP_Error( 'unexpected_update', 'Widget unexpectedly updated more than one option.' );
+				return new WP_Error( 'more_than_one_option_updated', __( 'Widget unexpectedly updated more than one option.' ) );
 			}
 
 			$updated_option_name = key( $options_transaction->options );
 			if ( $updated_option_name !== $option_name ) {
 				$options_transaction->rollback();
-				return new WP_Error( 'wrong_option', sprintf( 'Widget updated option "%1$s", but expected "%2$s".', $updated_option_name, $option_name ) );
+				// Translators: 1 is updated option name, 2 is expected option name.
+				return new WP_Error( 'wrong_option_updated', sprintf( __( 'Widget updated option "%1$s", but expected "%2$s".' ), $updated_option_name, $option_name ) );
 			}
 		}