lp-ugettext provides the language from browser via javascript. It's based in the piece of code of the Hamid posted in StackOverflow. It's was polymered! Stack
<body unresolved>
<!-- end elements -->
<lp-ugettext></lp-ugettext>
<script>
window.addEventListener('polymer-ready', function(e) {
var uget = document.querySelector('lp-ugettext');
console.log("mylanguage" + uget.language);
});
</script>
</body>