formatMessages(keys) {
    return this.formatWithFallback(keys, messageFromBundle);
  }
Format translations into `{value, attributes}` objects.

The fallback logic is the same as in `formatValues`
but it returns `{value, attributes}` objects
which are suitable for the translation of DOM elements.

Returns a Promise resolving to an array of the translation strings.

@example
```js
docL10n.formatMessages([
  {id: 'hello', args: { who: 'Mary' }},
  {id: 'welcome'}
]).then(console.log);

// [
//   { value: 'Hello, Mary!', attributes: null },
//   {
//     value: 'Welcome!',
//     attributes: [ { name: "title", value: 'Hello' } ]
//   }
// ]
```

@param   {Array<Object>} keys
@returns {Promise<Array<{value: string, attributes: Object}>>}
@private