I have detected my browser default language like this:
<script defer type="text/javascript">
(function(window, $) {
var lang = window.navigator.userLanguage || window.navigator.language;
alert(lang); // en_US
})(window, jQuery);
</script>
But I want to set my specific language(de_DE) on browser Chrome, Mozilla etc...
Do you have any idea?
You can't.
The browser language is the user's preference. Websites can't change it.
If you want to change the content of your website, then change the content (don't forget to update your lang attributes). This, obviously, won't affect the browser chrome.