DefaultLanguageItem.php

<?php

namespace Drupal\language;

use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Field\Plugin\Field\FieldType\LanguageItem;
use Drupal\Core\Language\Language;

/**
 * Alternative plugin implementation of the 'language' field type.
 *
 * Replaces the Core 'language' entity field type implementation, changes the
 * default values used.
 *
 * Required settings are:
 *  - target_type: The entity type to reference.
 *
 * @see language_field_info_alter().
 */
class DefaultLanguageItem extends LanguageItem {
    
    /**
     * {@inheritdoc}
     */
    public function applyDefaultValue($notify = TRUE) {
        // Default to LANGCODE_NOT_SPECIFIED.
        $langcode = Language::LANGCODE_NOT_SPECIFIED;
        if ($entity = $this->getEntity()) {
            $langcode = $this->getDefaultLangcode($entity);
        }
        // Always notify otherwise default langcode will not be set correctly.
        $this->setValue([
            'value' => $langcode,
        ], TRUE);
        return $this;
    }
    
    /**
     * Provides default language code of given entity.
     *
     * @param \Drupal\Core\Entity\EntityInterface $entity
     *   The entity whose language code to be loaded.
     *
     * @return string
     *   A string language code.
     */
    public function getDefaultLangcode(EntityInterface $entity) {
        return language_get_default_langcode($entity->getEntityTypeId(), $entity->bundle());
    }

}