LanguageConfigurationElement.php

<?php

namespace Drupal\language_elements_test\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\language\Entity\ContentLanguageSettings;

/**
 * A form containing a language configuration element.
 *
 * @internal
 */
class LanguageConfigurationElement extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'language_elements_configuration_element';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $conf = ContentLanguageSettings::loadByEntityTypeBundle('entity_test', 'some_bundle');
        $form['lang_configuration'] = [
            '#type' => 'language_configuration',
            '#entity_information' => [
                'entity_type' => 'entity_test',
                'bundle' => 'some_bundle',
            ],
            '#default_value' => $conf,
        ];
        $form['submit'] = [
            '#type' => 'submit',
            '#value' => 'Save',
        ];
        $form['#submit'][] = 'language_configuration_element_submit';
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
    }

}