//tin.php <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Untitled Document</title> </head> <body> <?php if(isset($_GET['lang'])) $lang=$_GET['lang']; else $lang="vi"; ?> <form id="form1" name="form1" method="get" action=""> <p> <label for="lang">Ngon ngu:</label> <select name="lang" id="lang" onchange="form1.submit()"> <option value="vi">Viet</option> <option value="en" <?php if($lang=="en") echo "selected";?>>English</option> </select> <...