Translation of custom body of email handler does not show as CKEditor

Thank you for your quick response and solution.

I tested the patch and it brings up the CKEditor as expected. Fantastic, this would suffice my use case!

There is actually the same kind of issue for the Confirmation message: a CKEditor field in the form settings, but a plain text field only in the translation form. Would it be possible to change this into a CKEditor field there as well?

If this is too complicated for general implementation - would it be possible to make such changes using a custom module?

@jrockowitz thank you for the hint. Your patch made me aware of the 'webform_html_editor' field type. Knowing that, it was quite easy to achieve having a CKEditor in the translation form elements of the confirmation message and email confirmation message, using a custom module.

Just wanted to share my solution on the example of the default Contact form, as it might be useful for someone else:

function MYMODULE_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {

  // Contact form translation
  if (($form_id == 'config_translation_edit_form' || $form_id == 'config_translation_add_form') && isset($form['config_names']['webform.webform.contact'])) {

    // Enable CKEditor for translation of confirmation message
    $form['config_names']['webform.webform.contact']['settings']['confirmation_message']['translation']['#type'] = 'webform_html_editor';
    // Enable CKEditor for translation of email confirmation message
    $form['config_names']['webform.webform.contact']['handlers']['email_confirmation']['settings']['body']['translation']['#type'] = 'webform_html_editor';
    // Enable CKEdtior for translation of email notification message
    $form['config_names']['webform.webform.contact']['handlers']['email_notification']['settings']['body']['translation']['#type'] = 'webform_html_editor';

  }
}

For other forms, the key 'webform.webform.contact' would need to be adapted.