user_mail

user_mail($key, &$message, $params)

function user_mail($key, &$message, $params) {
  $token_service = \Drupal::token();
  $language_manager = \Drupal::languageManager();
  $langcode = $message['langcode'];
  $variables = array('user' => $params['account']);

  $language = \Drupal::languageManager()->getLanguage($params['account']->getPreferredLangcode());
  $original_language = $language_manager->getConfigOverrideLanguage();
  $language_manager->setConfigOverrideLanguage($language);
  $mail_config = \Drupal::config('user.mail');

  $token_options = ['langcode' => $langcode, 'callback' => 'user_mail_tokens', 'clear' => TRUE];
  $message['subject'] .= PlainTextOutput::renderFromHtml($token_service->replace($mail_config->get($key . '.subject'), $variables, $token_options));
  $message['body'][] = $token_service->replace($mail_config->get($key . '.body'), $variables, $token_options);

  $language_manager->setConfigOverrideLanguage($original_language);

}