translateFragment(frag) {
    return this.translateElements(this.getTranslatables(frag));
  }
Translate a DOM element or fragment asynchronously using this
`DOMLocalization` object.

Manually trigger the translation (or re-translation) of a DOM fragment.
Use the `data-l10n-id` and `data-l10n-args` attributes to mark up the DOM
with information about which translations to use.

Returns a `Promise` that gets resolved once the translation is complete.

@param   {DOMFragment} frag - Element or DocumentFragment to be translated
@returns {Promise}