// These window.navigator contain language information
// 1. languages -> Array of preferred languages (eg ["en-US", "zh-CN", "ja-JP"]) Firefox^32, Chrome^32
// 2. language  -> Preferred language as String (eg "en-US") Firefox^5, IE^11, Safari, 
//                 Chrome sends Browser UI language
// 3. browserLanguage -> UI Language of IE
// 4. userLanguage    -> Language of Windows Regional Options
// 5. systemLanguage  -> UI Language of Windows
var browserLanguagePropertyKeys = ['languages', 'language', 'browserLanguage', 'userLanguage', 'systemLanguage'];

var availableLanguages = ['de', 'ar'];

var detectedLocale = _.chain(window.navigator)
    .pick(browserLanguagePropertyKeys) //Get only language properties
    .values() //Get values of the properties
    .flatten() //flatten all arrays
    .compact() //Remove undefined values
    .map(function (x) {
        return x.substr(0, 2); //Shorten strings to use two chars (en-US -> en)
    })
    .find(function (x) {
        return _.contains(availableLanguages, x); //Returns first language matched in available languages
    })
    .value();

var locale = detectedLocale || 'en'; //If no locale is detected, fallback to 'en'