title: How to detect user's language
body: <p>I'm going to detect user's keyboard language by javascript. I got a input (type of text) which should be filled with Persian characters. So, I need to alarm users change their keyboard language if their language is not Persian.</p>
  
  <p>What I have found is this:</p>
  
  <pre><code>window.navigator.language;
  </code></pre>
  
  <p>which detects browser's language which is always En-us.</p>
  
  <p>How could I solve that? </p>