Implements \Drupal\Core\Form\FormInterface::buildForm().
Overrides SystemConfigFormBase::buildForm
public function buildForm(array $form, array &$form_state) {
$config = $this->configFactory
->get('language.negotiation');
$form['selected_langcode'] = array(
'#type' => 'language_select',
'#title' => t('Language'),
'#languages' => Language::STATE_CONFIGURABLE | Language::STATE_SITE_DEFAULT,
'#default_value' => $config
->get('selected_langcode'),
);
return parent::buildForm($form, $form_state);
}