class DefaultLanguageItem

class DefaultLanguageItem extends LanguageItem {
  
  /**
   * {@inheritdoc}
   */
  public function applyDefaultValue($notify = TRUE) {
    $langcode = $this->getDefaultLanguageCode($this->getEntity()
      ->getEntityTypeId(), $this->getEntity()
      ->bundle());
    // Always notify otherwise default langcode will not be set correctly.
    $this->setValue([
      'value' => $langcode,
    ], TRUE);
    return $this;
  }
  
  /**
   * Provides default language code of a given an entity type and bundle.
   *
   * @param string $entity_type_id
   *   The entity type ID of the entity whose code of language is to be loaded.
   * @param string $bundle
   *   The entity bundle of the entity whose code of language is to be loaded.
   *
   * @return string
   *   A string language code.
   */
  protected function getDefaultLanguageCode(string $entity_type_id, string $bundle) : string {
    $language_manager = \Drupal::languageManager();
    $configuration = ContentLanguageSettings::loadByEntityTypeBundle($entity_type_id, $bundle);
    $default_value = NULL;
    $language_interface = $language_manager->getCurrentLanguage();
    switch ($configuration->getDefaultLangcode()) {
      case LanguageInterface::LANGCODE_SITE_DEFAULT:
        $default_value = $language_manager->getDefaultLanguage()
          ->getId();
        break;

      case 'current_interface':
        $default_value = $language_interface->getId();
        break;

      case 'authors_default':
        $user = \Drupal::currentUser();
        $language_code = $user->getPreferredLangcode();
        if (!empty($language_code)) {
          $default_value = $language_code;
        }
        else {
          $default_value = $language_interface->getId();
        }
        break;

    }
    if ($default_value) {
      return $default_value;
    }
    // If we still do not have a default value, just return the value stored in
    // the configuration; it has to be an actual language code.
    return $configuration->getDefaultLangcode();
  }
  
  /**
   * Provides default language code of given entity.
   *
   * @param \Drupal\Core\Entity\EntityInterface $entity
   *   The entity whose language code to be loaded.
   *
   * @return string
   *   A string language code.
   *
   * @deprecated in drupal:11.4.0 and is removed from drupal:13.0.0. There is no
   *   public replacement.
   *
   * @see https://www.drupal.org/node/3566774
   */
  public function getDefaultLangcode(EntityInterface $entity) {
    @trigger_error(__METHOD__ . '() is deprecated in drupal:11.4.0 and is removed from drupal:13.0.0. There is no public replacement. See https://www.drupal.org/node/3566774', E_USER_DEPRECATED);
    return $this->getDefaultLanguageCode($entity->getEntityTypeId(), $entity->bundle());
  }

}