class LanguageBlock

class LanguageBlock extends BlockBase implements ContainerFactoryPluginInterface, CacheOptionalInterface {
  
  /**
   * The language manager.
   *
   * @var \Drupal\Core\Language\LanguageManagerInterface
   */
  protected $languageManager;
  
  /**
   * The path matcher.
   *
   * @var \Drupal\Core\Path\PathMatcherInterface
   */
  protected $pathMatcher;
  
  /**
   * Constructs a LanguageBlock object.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin ID for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
   *   The language manager.
   * @param \Drupal\Core\Path\PathMatcherInterface $path_matcher
   *   The path matcher.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, LanguageManagerInterface $language_manager, PathMatcherInterface $path_matcher) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->languageManager = $language_manager;
    $this->pathMatcher = $path_matcher;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static($configuration, $plugin_id, $plugin_definition, $container->get('language_manager'), $container->get('path.matcher'));
  }
  
  /**
   * {@inheritdoc}
   */
  protected function blockAccess(AccountInterface $account) {
    $access = $this->languageManager
      ->isMultilingual() ? AccessResult::allowed() : AccessResult::forbidden();
    return $access->addCacheTags([
      'config:configurable_language_list',
    ]);
  }
  
  /**
   * {@inheritdoc}
   */
  public function build() {
    $build = [];
    $type = $this->getDerivativeId();
    $route_match = \Drupal::routeMatch();
    // If there is no route match, for example when creating blocks on 404 pages
    // for logged-in users with big_pipe enabled using the front page instead.
    if ($this->pathMatcher
      ->isFrontPage() || !$route_match->getRouteObject()) {
      // We are skipping the route match on both 404 and front page.
      // Example: If on front page, there is no route match like when creating
      // blocks on 404 pages for logged-in users with big_pipe enabled, use the
      // front page.
      $url = Url::fromRoute('<front>');
    }
    else {
      $url = Url::fromRouteMatch($route_match);
    }
    $links = $this->languageManager
      ->getLanguageSwitchLinks($type, $url);
    // In any render cache items wrapping this block, account for variations
    // by user access to each switcher link, the current path and query
    // arguments, and language negotiation.
    $cache_metadata = BubbleableMetadata::createFromRenderArray($build)->addCacheContexts([
      'url.path',
      'url.query_args',
      'url.site',
      'languages:' . $type,
    ]);
    if (isset($links->links)) {
      $build = [
        '#theme' => 'links__language_block',
        '#links' => $links->links,
        '#attributes' => [
          'class' => [
            "language-switcher-{$links->method_id}",
          ],
        ],
        '#set_active_class' => TRUE,
      ];
      foreach ($links->links as $link) {
        if ($link['url'] instanceof Url) {
          $cache_metadata->addCacheableDependency($link['url']->access(NULL, TRUE));
        }
      }
    }
    $cache_metadata->applyTo($build);
    return $build;
  }
  
  /**
   * {@inheritdoc}
   */
  public function createPlaceholder() : bool {
    return TRUE;
  }

}