Clarify order language behavior

I needed the language the user used to create the order.
I resorted to enabling the langcode field on commerce_order.

In a custom module:

function example_entity_type_build(array &$entity_types) {
  $keys = $entity_types['commerce_order']->getKeys();
  $keys['langcode'] = 'langcode';
  $entity_types['commerce_order']->set('entity_keys', $keys);
}

use Drupal\Core\Field\BaseFieldDefinition;
use Drupal\Core\StringTranslation\TranslatableMarkup;

/**
 * Add 'langcode' to 'commerce_order'.
 */
function example_update_8001() {
  $storage_definition = BaseFieldDefinition::create('language')
    ->setLabel(new TranslatableMarkup('Language'))
    ->setDisplayOptions('view', [
      'region' => 'hidden',
    ])
    ->setDisplayOptions('form', [
      'type' => 'language_select',
      'weight' => 2,
    ]);

  \Drupal::entityDefinitionUpdateManager()->installFieldStorageDefinition('langcode', 'commerce_order', 'commerce_order', $storage_definition);
}

This hold the current langcode when the order is first created.
After which it is accessible with $order->langcode()

I have the same problem but so far no solution.