/**
 * Implements hook_views_pre_render
 * @param \Drupal\views\ViewExecutable $view
 */
function gefic_programs_views_pre_render(\Drupal\views\ViewExecutable $view) {
  if($view->id() == 'programmes' && !empty($view->args)) {
    $termsTree = \Drupal::entityTypeManager()->getStorage('taxonomy_term')->loadTree('departement');
    // Get term by name
    foreach($termsTree as $termDpt) {
      if(\Drupal::service('pathauto.alias_cleaner')->cleanString($termDpt->name) == $view->args[0])
      {
        $term = $termDpt;
      }
    }

    if($term) {
      $term = \Drupal\taxonomy\Entity\Term::load($term->tid);
      // Force page title
      $newTitle = 'Nos programmes immobiliers : ' . $term->getName();
      $view->setTitle($newTitle);

      $request = \Drupal::request();
      if ($route = $request->attributes->get(\Symfony\Cmf\Component\Routing\RouteObjectInterface::ROUTE_OBJECT)) {
        $route->setDefault('_title', $newTitle);
      }
    }
  }
}

$termsTree = \Drupal::entityTypeManager()->getStorage('taxonomy_term')->loadTree('departement');

    foreach($termsTree as $termDpt) {
      if(\Drupal::service('pathauto.alias_cleaner')->cleanString($termDpt->name) == $params['arg_0'])
      {
        $term = $termDpt;
      }
    }

    if($term) {
      $term = \Drupal\taxonomy\Entity\Term::load($term->tid);

      $description = [
          '#tag' => 'meta',
          '#attributes' => [
              'name' => 'description',
              'content' => $term->label(),
          ],
      ];

      $variables['page']['#attached']['html_head'][] = [$description, 'description'];
    }