/**
 * Implements hook_query_TAG_alter(): tag search_$type with $type node_search.
 */    
function hook_query_search_node_search_alter(&$query) {
      $language = \Drupal::languageManager()->getCurrentLanguage()->getId();
      $query->condition('i.langcode', [$language, 'und', 'zxx'], 'IN');
}

/**
 * Implements hook_query_TAG_alter()
 */    
function hook_query_search_node_search_alter(&$query) {
      $language = \Drupal::languageManager()->getCurrentLanguage()->getId();
      $query->condition('i.langcode', [$language, 'und', 'zxx'], 'IN');
}