rootURL

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

router.js

import Ember from 'ember';
import config from './config/environment';

const Router = Ember.Router.extend({
  rootURL: '/es/'
});

Router.map(function() {
  this.route('index', { path: '/' });
  this.route('not-found', { path: '/*path' });
});

export default Router;

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

templates.index.hbs

Hello world!

templates.not-found.hbs

Not found!

twiddle.json

{
  "version": "0.7.2",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.2.2",
    "ember-data": "2.4.3",
    "ember-template-compiler": "2.2.2"
  }
}