How can get a non-trivial i18n translation to work using Sails.js?

Using Sails.js version 0.10.x and trying to get the i18n stuff to work.

I have the following in my config/locales/en.json

{
  "countries": {
    "au": {
      "name": "Australia",
      "fiatCurrency": "AUD",
      "subnationalDivisions": {
        "NSW": "New South Wales",
        "WA": "Western Australia",
        "VIC": "Victoria",
        "QLD": "Queensland",
        "TAS": "Tasmania",
        "SA": "South Australia",
        "NT": "Northern Territory",
        "ACT": "Australian Capital Territory"
      }
    }
  }
}

My config/i18n.js file looks like

module.exports.i18n = {

  // Which locales are supported?
  locales: ['en', 'es', 'fr', 'de'],

  objectNotation: true

};

In my controller I am trying to retrieve the correct subnationalDivision name via

res.i18n("countries." + country + ".subnationalDivisions." + state)

but that just gives me "countries.au.subnationalDivisions.ACT", not "Australian Capital Territory"

I've check with a trivial example:

Given en.json file containing { "bingo" : "sparky" }, res.i18n("bingo") outputs "sparky"

But examples using objectNotation don't work despite the instructions in the i18n-node documentation.

How should I get this to work?