automatic_updates-8.x-2.x-dev/tests/modules/automatic_updates_test/automatic_updates_test.module

<?php

/**
 * @file
 * Contains hook implementations for testing Automatic Updates.
 */

declare(strict_types=1);

use Drupal\Core\StringTranslation\TranslatableMarkup;

/**
 * Implements hook_mail_alter().
 */
function automatic_updates_test_mail_alter(array &$message): void {
  if (str_starts_with($message['id'], 'automatic_updates_')) {
    $line_langcodes = [];

    // Get the langcode of every translated line in the message, including the
    // subject line.
    $lines = array_merge($message['body'], [
      $message['subject'],
    ]);
    foreach ($lines as $line) {
      if ($line instanceof TranslatableMarkup) {
        $line_langcodes[] = $line->getOption('langcode');
      }
    }
    $message['line_langcodes'] = array_unique($line_langcodes);
  }
}