JavaScript for detecting browser language preference [duplicate]

Answer 1

Based on the answer here Accessing the web page's HTTP Headers in JavaScript I built the following script to get the browser language:

var req = new XMLHttpRequest();
req.open('GET', document.location, false);
req.send(null);
var headers = req.getAllResponseHeaders().toLowerCase();
var contentLanguage = headers.match( /^content-language\:(.*)$/gm );
if(contentLanguage[0]) {
    return contentLanguage[0].split(":")[1].trim().toUpperCase();
}