class LanguageReference

class LanguageReference extends DataReferenceBase {
    
    /**
     * {@inheritdoc}
     */
    public function getTargetIdentifier() {
        $language = $this->getTarget();
        return isset($language) ? $language->id() : NULL;
    }
    
    /**
     * Returns all valid values for a `langcode` config value.
     *
     * @return string[]
     *   All possible valid langcodes. This includes all langcodes in the standard
     *   list of human languages, along with special langcodes like `und`, `zxx`,
     *   and `site_default`, which Drupal uses internally. If any custom languages
     *   are defined, they will be included as well.
     *
     * @see \Drupal\Core\Language\LanguageManagerInterface::getLanguages()
     * @see \Drupal\Core\Language\LanguageManagerInterface::getStandardLanguageList()
     */
    public static function getAllValidLangcodes() : array {
        $language_manager = \Drupal::languageManager();
        return array_unique([
            array_keys($language_manager::getStandardLanguageList()),
            // We can't use LanguageInterface::STATE_ALL because it will exclude the
            // site default language in certain situations.
            // @see \Drupal\Core\Language\LanguageManager::filterLanguages()
array_keys($language_manager->getLanguages(LanguageInterface::STATE_LOCKED | LanguageInterface::STATE_CONFIGURABLE | LanguageInterface::STATE_SITE_DEFAULT)),
            // Include special language codes used internally.
LanguageInterface::LANGCODE_NOT_APPLICABLE,
            LanguageInterface::LANGCODE_SITE_DEFAULT,
            LanguageInterface::LANGCODE_DEFAULT,
            LanguageInterface::LANGCODE_SYSTEM,
            LanguageInterface::LANGCODE_NOT_SPECIFIED,
        ]);
    }

}