function wp_update_themes( $extra_stats = array() ) {
  if ( wp_installing() ) {
    return;
  }

  // Include an unmodified $wp_version.
  require ABSPATH . WPINC . '/version.php';

  $installed_themes = wp_get_themes();
  $translations     = wp_get_installed_translations( 'themes' );

  $last_update = get_site_transient( 'update_themes' );

  if ( ! is_object( $last_update ) ) {
    $last_update = new stdClass;
  }

  $themes  = array();
  $checked = array();
  $request = array();

  // Put slug of active theme into request.
  $request['active'] = get_option( 'stylesheet' );

  foreach ( $installed_themes as $theme ) {
    $checked[ $theme->get_stylesheet() ] = $theme->get( 'Version' );

    $themes[ $theme->get_stylesheet() ] = array(
      'Name'       => $theme->get( 'Name' ),
      'Title'      => $theme->get( 'Name' ),
      'Version'    => $theme->get( 'Version' ),
      'Author'     => $theme->get( 'Author' ),
      'Author URI' => $theme->get( 'AuthorURI' ),
      'UpdateURI'  => $theme->get( 'UpdateURI' ),
      'Template'   => $theme->get_template(),
      'Stylesheet' => $theme->get_stylesheet(),
    );
  }

  $doing_cron = wp_doing_cron();

  // Check for update on a different schedule, depending on the page.
  switch ( current_filter() ) {
    case 'upgrader_process_complete':
      $timeout = 0;
      break;
    case 'load-update-core.php':
      $timeout = MINUTE_IN_SECONDS;
      break;
    case 'load-themes.php':
    case 'load-update.php':
      $timeout = HOUR_IN_SECONDS;
      break;
    default:
      if ( $doing_cron ) {
        $timeout = 2 * HOUR_IN_SECONDS;
      } else {
        $timeout = 12 * HOUR_IN_SECONDS;
      }
  }

  $time_not_changed = isset( $last_update->last_checked ) && $timeout > ( time() - $last_update->last_checked );

  if ( $time_not_changed && ! $extra_stats ) {
    $theme_changed = false;

    foreach ( $checked as $slug => $v ) {
      if ( ! isset( $last_update->checked[ $slug ] ) || (string) $last_update->checked[ $slug ] !== (string) $v ) {
        $theme_changed = true;
      }
    }

    if ( isset( $last_update->response ) && is_array( $last_update->response ) ) {
      foreach ( $last_update->response as $slug => $update_details ) {
        if ( ! isset( $checked[ $slug ] ) ) {
          $theme_changed = true;
          break;
        }
      }
    }

    // Bail if we've checked recently and if nothing has changed.
    if ( ! $theme_changed ) {
      return;
    }
  }

  // Update last_checked for current to prevent multiple blocking requests if request hangs.
  $last_update->last_checked = time();
  set_site_transient( 'update_themes', $last_update );

  $request['themes'] = $themes;

  $locales = array_values( get_available_languages() );

  
/**
 * Filters the locales requested for theme translations.
 *
 * @since 3.7.0
 * @since 4.5.0 The default value of the `$locales` parameter changed to include all locales.