php menu setting for language settings

Question 1

This fragment of code:

<?php $string = basename(__FILE__); ?>
<?php echo "<a href=".$string.'?lang=en >';  $_SESSION['lang']= 'en'; ?><img src="images/en.png" /></a>
<?php echo "<a href=".$string.'?lang=hk >';  $_SESSION['lang']= 'hk'; ?><img src="images/hk.png" /></a>
<?php echo "<a href=".$string.'?lang=cn >';  $_SESSION['lang']= 'cn'; ?><img src="images/cn.png" /></a>

Will always set your $_SESSION['lang'] to cn value, not only when you click certain anchor. Instead you should change it to:

<?php $string = basename(__FILE__); ?>
<a href="<?php echo $string; ?>?lang=en"><img src="images/en.png" /></a>
<a href="<?php echo $string; ?>?lang=hk"><img src="images/hk.png" /></a>
<a href="<?php echo $string; ?>?lang=cn"><img src="images/cn.png" /></a>

And also at the beginning of the file you should add:

<?php
if(!isset($_SESSION['lang']))
    $_SESSION['lang'] = 'cn'; // Sets default language to 'cn'

if(isset($_GET['lang']) && in_array($_GET['lang'], array('en', 'hk', 'cn')))
    $_SESSION['lang'] = $_GET['lang']; // Sets language based on URL
?>

Don't forget to add session_start() at the beginning, before previously mentioned block of code aswell, if you don't have it yet.

From now on, if you won't have ?lang=... in your URL, you will have your last lang set in $_SESSION['lang'].

To change links in the other menu (<li><a href="index.php"><?php echo $lang['MENU_HOME']; ?></a></li> and so on), you should change their href's from:

<li><a href="filename.php"><?php echo $lang['MENU_HOME']; ?></a></li>

To:

<li><a href="filename.php?lang=<?php echo $_SESSION['lang']; ?>"><?php echo $lang['MENU_HOME']; ?></a></li>

Question 2

Best was to keep desired language selected is using $_SESSION variable.

Clicking on your menu link with ?lang=en should redirrect to any script, where you catch $_GET['lang'] variable and insert it into $_SESSION['lang'] variable.

Then you can simply look into $_SESSION['lang'] variable to get current language and this variable is global so you can access it from anywhere.

session_start();
if($_GET && $_GET['lang']){
  $_SESSION['lang'] = $_GET['lang'];
}