Browser language detection

browser-language.js

// Returns first configured browser language.
const lang = navigator.language || navigator.userLanguage;

return lang.split('-').shift();

// Returns comma separated list of languages.
let lang = (navigator.languages && 0 !== navigator.languages.length
  ? navigator.languages
  : [navigator.language || navigator.userLanguage || 'en']);

lang = lang.map(function (lan) {
  return lan.split('-').shift();
});

return lang.filter(function (e, n) {
  return lang.indexOf(e) === n;
});