class LanguageServiceProvider

class LanguageServiceProvider extends ServiceProviderBase {
  const CONFIG_PREFIX = 'language.entity.';

  /**
   * {@inheritdoc}
   */
  public function register(ContainerBuilder $container) {

    // The following services are needed only on multilingual sites.
    if ($this
      ->isMultilingual()) {
      $container
        ->register('language_request_subscriber', 'Drupal\\language\\EventSubscriber\\LanguageRequestSubscriber')
        ->addTag('event_subscriber')
        ->addArgument(new Reference('language_manager'))
        ->addArgument(new Reference('language_negotiator'))
        ->addArgument(new Reference('string_translation'))
        ->addArgument(new Reference('current_user'));
      $container
        ->register('path_processor_language', 'Drupal\\language\\HttpKernel\\PathProcessorLanguage')
        ->addTag('path_processor_inbound', [
        'priority' => 300,
      ])
        ->addTag('path_processor_outbound', [
        'priority' => 100,
      ])
        ->addArgument(new Reference('config.factory'))
        ->addArgument(new Reference('language_manager'))
        ->addArgument(new Reference('language_negotiator'))
        ->addArgument(new Reference('current_user'))
        ->addArgument(new Reference('language.config_subscriber'))
        ->addMethodCall('initConfigSubscriber');
    }
  }

  /**
   * {@inheritdoc}
   */
  public function alter(ContainerBuilder $container) {
    $definition = $container
      ->getDefinition('language_manager');
    $definition
      ->setClass('Drupal\\language\\ConfigurableLanguageManager')
      ->addArgument(new Reference('config.factory'))
      ->addArgument(new Reference('module_handler'))
      ->addArgument(new Reference('language.config_factory_override'))
      ->addArgument(new Reference('request_stack'));
    if ($default_language_values = $this
      ->getDefaultLanguageValues()) {
      $container
        ->setParameter('language.default_values', $default_language_values);
    }
  }

  /**
   * Checks whether the site is multilingual.
   *
   * @return bool
   *   TRUE if the site is multilingual, FALSE otherwise.
   */
  protected function isMultilingual() {

    // Assign the prefix to a local variable so it can be used in an anonymous
    // function.
    $prefix = static::CONFIG_PREFIX;

    // @todo Try to swap out for config.storage to take advantage of database
    //   and caching. This might prove difficult as this is called before the
    //   container has finished building.
    $config_storage = BootstrapConfigStorageFactory::get();
    $config_ids = array_filter($config_storage
      ->listAll($prefix), function ($config_id) use ($prefix) {
      return $config_id != $prefix . LanguageInterface::LANGCODE_NOT_SPECIFIED && $config_id != $prefix . LanguageInterface::LANGCODE_NOT_APPLICABLE;
    });
    return count($config_ids) > 1;
  }

  /**
   * Gets the default language values.
   *
   * @return array|bool
   *   Returns the default language values for the language configured in
   *   system.site:default_langcode if the corresponding configuration entity
   *   exists, otherwise FALSE.
   */
  protected function getDefaultLanguageValues() {
    $config_storage = BootstrapConfigStorageFactory::get();
    $system = $config_storage
      ->read('system.site');

    // In Kernel tests it's possible this code is called before system.site
    // exists. In such cases behave as though the corresponding language
    // configuration entity does not exist.
    if ($system === FALSE) {
      return FALSE;
    }
    $default_language = $config_storage
      ->read(static::CONFIG_PREFIX . $system['default_langcode']);
    if (is_array($default_language)) {
      return $default_language;
    }
    return FALSE;
  }

}