code: protected static function loadMappings()
      {
          // check status
          self::checkStatus();
  
          // mapping cache loaded already for $class
          if (static::hasMappings()) {
              return;
          }
  
          // load $class mapping
          $loadedClass = static::hasLoader(true);
          static::setMappings(
              $loadedClass ?
                  $loadedClass::getLoader()->loadMessages(get_called_class()) : [],
              false
          );
      }
docs: Load message mappings into cache for $class
  
  @access protected