ContentTranslationManageAccessCheck::access

public ContentTranslationManageAccessCheck::access(Route $route, RouteMatchInterface $route_match, AccountInterface $account, $source = NULL, $target = NULL, $language = NULL, $entity_type_id = NULL)

public function access(Route $route, RouteMatchInterface $route_match, AccountInterface $account, $source = NULL, $target = NULL, $language = NULL, $entity_type_id = NULL) {
  /* @var \Drupal\Core\Entity\ContentEntityInterface $entity */
  if ($entity = $route_match->getParameter($entity_type_id)) {
    $operation = $route->getRequirement('_access_content_translation_manage');
    $language = $this->languageManager->getLanguage($language) ? : $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_CONTENT);
    $entity_type = $this->entityManager->getDefinition($entity_type_id);

    if (in_array($operation, ['update', 'delete'])) {
      // Translation operations cannot be performed on the default
      // translation.
      if ($language->getId() == $entity->getUntranslated()->language()->getId()) {
        return AccessResult::forbidden()->addCacheableDependency($entity);
      }
      // Editors have no access to the translation operations, as entity
      // access already grants them an equal or greater access level.
      $templates = ['update' => 'edit-form', 'delete' => 'delete-form'];
      if ($entity->access($operation) && $entity_type->hasLinkTemplate($templates[$operation])) {
        return AccessResult::forbidden()->cachePerPermissions();
      }
    }

    if ($account->hasPermission('translate any entity')) {
      return AccessResult::allowed()->cachePerPermissions();
    }

    /* @var \Drupal\content_translation\ContentTranslationHandlerInterface $handler */
    $handler = $this->entityManager->getHandler($entity->getEntityTypeId(), 'translation');

    // Load translation.
    $translations = $entity->getTranslationLanguages();
    $languages = $this->languageManager->getLanguages();

    switch ($operation) {
      case 'create':
        $source_language = $this->languageManager->getLanguage($source) ? : $entity->language();
        $target_language = $this->languageManager->getLanguage($target) ? : $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_CONTENT);
        $is_new_translation = ($source_language->getId() != $target_language->getId()
          && isset($languages[$source_language->getId()])
          && isset($languages[$target_language->getId()])
          && !isset($translations[$target_language->getId()]));
        return AccessResult::allowedIf($is_new_translation)->cachePerPermissions()->addCacheableDependency($entity)
          ->andIf($handler->getTranslationAccess($entity, $operation));

      case 'delete':
      case 'update':
        $has_translation = isset($languages[$language->getId()])
          && $language->getId() != $entity->getUntranslated()->language()->getId()
          && isset($translations[$language->getId()]);
        return AccessResult::allowedIf($has_translation)->cachePerPermissions()->addCacheableDependency($entity)
          ->andIf($handler->getTranslationAccess($entity, $operation));
    }
  }

  // No opinion.
  return AccessResult::neutral();
}