The page looks broken because the paths are wrong, as the page assumes it’s in the top-level of the webserver, i.e. http://locahost, not http://locahost/lang/www. So you either need to put it in the top-level web directory or you configure a virtual server whose top-level directory is the directory where you have put LT. I don’t know XAMPP, so I cannot tell you how that is done.
3/ My problem now is that I cannot enter text into text area because it seems dont have a text edit area here which should be included in stage-head.php as in the picture below:
4/ I think the path to checkform.php is incorrect, so I changed to …/checkform.php (just jump up one level from stage-head.php and see checkform.php). I got this error, however.
I think this might be a Javascript issue instead, I suggest you undo your change and use F12 to get to the console in your browser so you can see if there are JS errors.