class ConfigTranslationFormAccess

class ConfigTranslationFormAccess extends ConfigTranslationOverviewAccess {
    
    /**
     * Checks access to the overview based on permissions and translatability.
     *
     * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
     *   The route_match to check against.
     * @param \Drupal\Core\Session\AccountInterface $account
     *   The account to check access for.
     * @param string $langcode
     *   The language code of the target language.
     *
     * @return \Drupal\Core\Access\AccessResultInterface
     *   The access result.
     */
    public function access(RouteMatchInterface $route_match, AccountInterface $account, $langcode = NULL) {
        $mapper = $this->getMapperFromRouteMatch($route_match);
        try {
            $source_langcode = $mapper->getLangcode();
            $source_language = $this->languageManager
                ->getLanguage($source_langcode);
            $target_language = $this->languageManager
                ->getLanguage($langcode);
            return $this->doCheckAccess($account, $mapper, $source_language, $target_language);
        } catch (ConfigMapperLanguageException $exception) {
            return AccessResult::forbidden();
        }
    }
    
    /**
     * Checks access given an account, configuration mapper, and source language.
     *
     * In addition to the checks performed by
     * ConfigTranslationOverviewAccess::doCheckAccess() this makes sure the target
     * language is not locked and the target language is not the source language.
     *
     * Although technically configuration can be overlaid with translations in the
     * same language, that is logically not a good idea.
     *
     * @param \Drupal\Core\Session\AccountInterface $account
     *   The account to check access for.
     * @param \Drupal\config_translation\ConfigMapperInterface $mapper
     *   The configuration mapper to check access for.
     * @param \Drupal\Core\Language\LanguageInterface|null $source_language
     *   The source language to check for, if any.
     * @param \Drupal\Core\Language\LanguageInterface|null $target_language
     *   The target language to check for, if any.
     *
     * @return \Drupal\Core\Access\AccessResultInterface
     *   The result of the access check.
     *
     * @see \Drupal\config_translation\Access\ConfigTranslationOverviewAccess::doCheckAccess()
     */
    protected function doCheckAccess(AccountInterface $account, ConfigMapperInterface $mapper, $source_language = NULL, $target_language = NULL) {
        $base_access_result = parent::doCheckAccess($account, $mapper, $source_language);
        $access = $target_language && !$target_language->isLocked() && (!$source_language || $target_language->getId() !== $source_language->getId());
        return $base_access_result->andIf(AccessResult::allowedIf($access));
    }

}