Confirmation mail after registration in language of the user

Hello,

I added the following code (from another post within this forum) to my site that allows the user to choose his preferred language during the registration process:

function mymodule_form_alter($form, &$form_state, $form_id) {
    if ($form_id == 'user_register') {
        global $language;
        $languages = language_list('enabled');
        $languages = $languages[1];

        // If the user is being created, we set the user language to the page language.
        //$user_preferred_language = $user ? user_preferred_language($user) : $language;
        $user_preferred_language = $language;

        $names = array();
        foreach ($languages as $langcode => $item) {
          $name = t($item->name);
          $names[$langcode] = $name . ($item->native != $name ? ' ('. $item->native .')' : '');
        }
        $form['locale'] = array(
          '#type' => 'fieldset',
          '#title' => t('Language settings'),
          '#weight' => 1,
        );

        $form['locale']['language'] = array(
          '#type' => (count($names) <= 5 ? 'radios' : 'select'),
          '#title' => t('Language'),
          '#default_value' => $user_preferred_language->language,
          '#options' => $names,
          '#description' => t("This account's default language for e-mails."),
        );
    }
}

The user can select his preferred language:

• English
• German

If he select German, the confirmation mail is still in English. I translated the strings from the "User settings" page that are within the "Welcome, no approval required" field to German ("Translate interface").

Do you have any idea why the system still sends the confirmation mail in English and not in German?

Many thanks,
Faustas