Sub request doesn't take care of the language

Question

I have defined a route as follow:

mymodule.node_summary:
  path: '/node/{node}/summary'
  options:
    parameters:
      node:
        type: 'entity:node'
  defaults:
    _controller: '\Drupal\mymodule\Controller\NodeSummaryController::content'
    _title: 'Summary'
  requirements:
    node: \d+
    _entity_access: 'node.view'

Then I have created the following controller:

class NodeSummaryController {

  public function content(Node $node = NULL) {
    $view_builder = Drupal::entityTypeManager()
      ->getViewBuilder('node');
    $summary = $view_builder->view($node, 'summary');
    $render = Drupal::service('renderer')
      ->renderPlain($summary);
    $response = new Response($render);
    return $response;
  }
}

If I visit the page /nl/node/xxx/summary everything is fine, my node's summary is displayed in dutch

But if I try to get this content with a sub-request, I get the result in the default language of my site, not in dutch

  $kernel = \Drupal::service('http_kernel.basic');
  $sub_request = \Symfony\Component\HttpFoundation\Request::create("/nl/node/xxx/summary");
  $response = $kernel->handle($sub_request, \Symfony\Component\HttpKernel\HttpKernelInterface::SUB_REQUEST);
  $html = $response->getContent();
  dpm($html); // ERROR THIS IS NOT IN DUTCH

Answer 1

I was a bit overly optimistic in the previous question suggesting a sub-request. The language manager service doesn't store data in such a way that it can run within a sub-request scope. So it seems you need to do the same as in the previous question, only that now the interface translation works without a custom negotiator by resetting the language manager (and also the string translation service, see the comment) before running the sub-request:

$language_manager = \Drupal::languageManager();

$langcode = 'nl';
$language = $language_manager->getLanguage($langcode);
$original_language = $language_manager->getConfigOverrideLanguage();
$language_manager->reset();
\Drupal::service('string_translation')->setDefaultLangcode($langcode);
$language_manager->setConfigOverrideLanguage($language);
\Drupal::service('entity_field.manager')->clearCachedFieldDefinitions();

$kernel = \Drupal::service('http_kernel.basic');
$sub_request = \Symfony\Component\HttpFoundation\Request::create('/' . $langcode . '/node/1/summary');
$response = $kernel->handle($sub_request, \Symfony\Component\HttpKernel\HttpKernelInterface::SUB_REQUEST);

$language_manager->reset();
$current_language = $language_manager->getCurrentLanguage();
\Drupal::service('string_translation')->setDefaultLangcode($current_language->getId());
$language_manager->setConfigOverrideLanguage($original_language);
\Drupal::service('entity_field.manager')->clearCachedFieldDefinitions();

$html = $response->getContent();