Extjs I18n (Keys & Translations stored in application itself)

I18n.js

Ext.define('App.common.I18n', {
    singleton: true,
    alternateClassName: ['I18n'],
    requires: [
        'App.locale.locale-de',
        'App.locale.locale-en',
        'App.locale.locale-fr',
        'App.locale.locale-it'
    ],
    initLocale: function () {
        var pageParameters = Ext.urlDecode(window.location.search.substring(1));
        // check in url
        if (pageParameters.lang && (pageParameters.lang === 'en' || pageParameters.lang === 'de' || pageParameters.lang === 'fr' || pageParameters.lang === 'it')) {
            localStorage.setItem('userLanguage', pageParameters.lang);
            this.locale = pageParameters.lang;
        } else {
            // check in localStorage
            var storedLocale = localStorage.getItem('userLanguage');
            this.locale = storedLocale ? storedLocale : 'en';
        }
    },
    get: function (key) {
        if (!this.locale) {
            this.initLocale();
        }
        switch (this.locale) {
            case 'en': {
                return EN.Labels[key] ? EN.Labels[key] : key;
            }
            case 'de': {
                return DE.Labels[key] ? DE.Labels[key] : key;
            }
            case 'fr': {
                return FR.Labels[key] ? FR.Labels[key] : key;
            }
            case 'it': {
                return IT.Labels[key] ? IT.Labels[key] : key;
            }
            default: return EN.Labels[key] ? EN.Labels[key] : key;
        }
    },
    getYesNo: function (value) {
        return value === true ? this.get('Common.Label.Yes') : this.get('Common.Label.No');
    },
    getYesNoInternet: function (value) {
        return value === true ? this.get('Common.Label.YesInternet') : this.get('Common.Label.NoInternet');
    },
    getOnOff: function (value) {
        return value === true ? this.get('Common.Label.On') : this.get('Common.Label.Off');
    },
    getOnOffNotPossible: function (value) {
        if (!value) {
            return value;
        }
        if (value === 'ON') {
            return this.get('Common.Label.On');
        } else if (value === 'OFF') {
            return this.get('Common.Label.Off');
        }
        return this.get('Common.Label.NotPossible');
    },
    locale: null    
});

locale-en.js

Ext.define('App.locale.locale-en', {
  singleton: true,
  alternateClassName: ['EN'],
  constructor: function (config) {
    this.initConfig(config);
  },
  Labels: {
     'Common.Label.Yes': 'Yes',
    'Common.Label.No': 'No',
    'Common.Label.Off': 'Off',
    'Common.Label.On': 'On',
    'Common.Label.NotPossible': 'Not possible',
  }
});