PoDatabaseReader example

  public function submitForm(array &$form, FormStateInterface $form_state) {
    // If template is required, language code is not given.     if ($form_state->getValue('langcode') != LanguageInterface::LANGCODE_SYSTEM) {
      $language = $this->languageManager->getLanguage($form_state->getValue('langcode'));
    }
    else {
      $language = NULL;
    }
    $content_options = $form_state->getValue('content_options', []);
    $reader = new PoDatabaseReader();
    $language_name = '';
    if ($language != NULL) {
      $reader->setLangcode($language->getId());
      $reader->setOptions($content_options);
      $languages = $this->languageManager->getLanguages();
      $language_name = isset($languages[$language->getId()]) ? $languages[$language->getId()]->getName() : '';
      $filename = $language->getId() . '.po';
    }
    else {
      // Template required.       $filename = 'drupal.pot';
    }