ember-i18n did not find a default locale; falling back to "en"

I am getting this warning for ember-i18n ("ember-i18n": "5.0.0")

//environment.js

module.exports = function(environment) {
   var ENV = { **removed default code** };
   ENV.i18n = { defaultLocale: 'en' };

   return ENV;
}

//package.json

{
  "devDependencies": {
      "ember-i18n": "5.0.0"
  }
}

//app/initializer/i18n.js

import Ember from 'ember';

export default {
    name: 'i18n',
    after: 'ember-i18n',
    initialize: function()
    {
        var application = arguments[1] || arguments[0];
        application.inject('controller', 'i18n', 'service:i18n');
        application.inject('route', 'i18n', 'service:i18n');
    }
}