declarative translations

components.my-translation.js

import Ember from 'ember';
const { computed } = Ember;

export default Ember.Component.extend({
  content: computed('translation.content', function() {
  	if ('then' in translation) {
      return translation.content;
    } else {
      return translation;
    }
  }),
}).reopenClass({
	positionalParams: ['translation']
});

controllers.application.js

import Ember from 'ember';
import emulateTranslationLoad from '../utils/load-t';
const {
  Controller,
  computed,
  ObjectProxy,
  PromiseProxyMixin
} = Ember;

let ObjectPromiseProxy = ObjectProxy.extend(PromiseProxyMixin);

function translation(key) {
  return computed(function() {
    return ObjectPromiseProxy.create({
      promise: emulateTranslationLoad(key)
    }); 
  });
}

export default Controller.extend({
  appName: translation('appName'),

  brokenTranslation: translation('blabla')
});

templates.application.hbs

<h1>Welcome to {{my-translation appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br />

templates.components.my-translation.hbs

{{#if translation.isPending}}
  Loading translation...
{{else}}
	{{#if translation.isRejected}}
  	Failed to load translation...
	{{else}}
  	{{translation.content}}
  {{/if}}
{{/if}}

twiddle.json

{
  "version": "0.10.6",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.9.0",
    "ember-data": "2.9.0",
    "ember-template-compiler": "2.9.0",
    "ember-testing": "2.9.0"
  },
  "addons": {}
}

utils.load-t.js

import Ember from 'ember';
const {
  RSVP,
  run
} = Ember;

const Translations = {
  appName: 'Ember Twiddle'
};

export default function emulateTranslationLoad(key) {
  return new RSVP.Promise((resolve, reject) => {
    run.later(this, () => {
      if (key in Translations) {
        resolve(Translations[key]);
      } else {
        reject()
      }
    }, 300);
  });
};