public function validateForm(array &$form, FormStateInterface $form_state) {
parent::validateForm($form, $form_state);
if (!$form_state
->getValue('plugin')) {
$form_state
->setErrorByName('plugin', $this
->t('You have to select a translator plugin.'));
}
$plugin_ui = $this->translatorManager
->createUIInstance($this->entity
->getPluginID());
$plugin_ui
->validateConfigurationForm($form, $form_state);
}