Terms aggregates labels are not evaluated

For example:

1. if one defines a custom type names author in Studio (see authorDoc.png)
2. then a terms aggregate on the primaryType (see primaryTypeAggregate.png)
3. no label is shown in the results (see noLabel.png)

The network trace in Google Inspector shows the following results:

      "buckets": [
        {
          "key": "Author",
          "fetchedKey": "Author",
          "docCount": 3
        },
        {
          "key": "File",
          "fetchedKey": "File",
          "docCount": 1
        }
      ],
      "extendedBuckets": [
        {
          "key": "Author",
          "fetchedKey": "Author",
          "docCount": 3
        },
        {
          "key": "File",
          "fetchedKey": "File",
          "docCount": 1
        }
      ]

but there is no i18n evaluation in the nuxeo-checkbox-aggregation element:
https://github.com/nuxeo/nuxeo-ui-elements/blob/maintenance-2.2.x/nuxeo-aggregation/nuxeo-checkbox-aggregation.html#L53
whereas there is one for the empty result message:
https://github.com/nuxeo/nuxeo-ui-elements/blob/maintenance-2.2.x/nuxeo-aggregation/nuxeo-checkbox-aggregation.html#L57

Expected behavior: there should be an i18n evaluation. This would allow to add an entry like this:

"Author": "my nice author label"

in the messages.json file
Workaround: none since the element is vulkanized and thus cannot be overriden