locale_form_language_admin_add_form_alter_submit

locale_form_language_admin_add_form_alter_submit($form, FormStateInterface $form_state)

function locale_form_language_admin_add_form_alter_submit($form, FormStateInterface $form_state) {
  \Drupal::moduleHandler()->loadInclude('locale', 'fetch.inc');
  $options = _locale_translation_default_update_options();

  if ($form_state->isValueEmpty('predefined_langcode') || $form_state->getValue('predefined_langcode') == 'custom') {
    $langcode = $form_state->getValue('langcode');
  }
  else {
    $langcode = $form_state->getValue('predefined_langcode');
  }

  if (\Drupal::config('locale.settings')->get('translation.import_enabled')) {
    // Download and import translations for the newly added language.
    $batch = locale_translation_batch_update_build(array(), array($langcode), $options);
    batch_set($batch);
  }

  // Create or update all configuration translations for this language. If we
  // are adding English then we need to run this even if import is not enabled,
  // because then we extract English sources from shipped configuration.
  if (\Drupal::config('locale.settings')->get('translation.import_enabled') || $langcode == 'en') {
    \Drupal::moduleHandler()->loadInclude('locale', 'bulk.inc');
    if ($batch = locale_config_batch_update_components($options, array($langcode))) {
      batch_set($batch);
    }
  }
}