How can I get and parse Accept Header to get language at JavaScript?

How can I get and parse Accept Header to get language as two character => en, tr, ar, fr, etc. at JavaScript?

EDIT: When I use

navigator.language

or something like that it gives me a language. However I am using a plug-in at Firefox, Quick Locale, it changes the local. When I change it from English to Arabic, still navigator.language says that I am using English. However when I connect to www.google.com, after I changed locale with 开发者_JS百科Quick Locale, Google's homepage opens at Arabic language. I want to detect the user's language as like that. I will load the language properties of my HTML file after I detected the language as like Google.

EDIT2: There is a code for my purpose here: accept header script

However it makes a call to that URL: http://ajaxhttpheaders.appspot.com

How can I get the source code at that URL?

EDIT3: Can I write something similar to that code at my server side (to communicate my HTML side via REST - this is last solution for me) ?

You can't. But you can try to detect browser language.

Edit: If you would like to change site content depending on accept header (like google) then you have to do it on server side.