LanguageFilter.php

<?php

namespace Drupal\views\Plugin\views\filter;

use Drupal\Core\Language\LanguageInterface;
use Drupal\Core\Language\LanguageManagerInterface;
use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
use Drupal\Core\Session\AccountInterface;
use Drupal\views\Attribute\ViewsFilter;
use Drupal\views\Plugin\views\PluginBase;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * Provides filtering by language.
 *
 * @ingroup views_filter_handlers
 */

#[ViewsFilter("language")]
class LanguageFilter extends InOperator implements ContainerFactoryPluginInterface {

  /**
   * The language manager.
   *
   * @var \Drupal\Core\Language\LanguageManagerInterface
   */
  protected $languageManager;

  /**
   * Constructs a new LanguageFilter instance.
   *
   * @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 $language_manager
   *   The language manager.
   */
  public function __construct($configuration, $plugin_id, $plugin_definition, LanguageManagerInterface $language_manager) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->languageManager = $language_manager;
  }

  /**
   * {@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'));
  }

  /**
   * {@inheritdoc}
   */
  public function getValueOptions() {
    if (!isset($this->valueOptions)) {
      $this->valueTitle = $this
        ->t('Language');

      // Pass the current values so options that are already selected do not get
      // lost when there are changes in the language configuration.
      $this->valueOptions = $this
        ->listLanguages(LanguageInterface::STATE_ALL | LanguageInterface::STATE_SITE_DEFAULT | PluginBase::INCLUDE_NEGOTIATED, array_keys($this->value));
    }
    return $this->valueOptions;
  }

  /**
   * {@inheritdoc}
   */
  public function query() {

    // No point in displaying the language filter on monolingual sites,
    // as only one language value is available.
    if (!$this->languageManager
      ->isMultilingual()) {
      return;
    }
    parent::query();
  }

  /**
   * {@inheritdoc}
   */
  public function access(AccountInterface $account) : bool {
    return $this->languageManager
      ->isMultilingual() && parent::access($account);
  }

}