This is an example of this you want:
<?
session_start();
if ($_GET["lang"]=="greek")
{
$_SESSION["swf"]="greek.swf";
}
else
$_SESSION["swf"]="english.swf";
?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Untitled Document</title>
</head>
<body>
<p><a href="?lang=eng">English</a> <a href="?lang=greek">Greek</a></p>
<p>
<object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,29,0" width="85" height="40">
<param name="movie" value="<? echo $_SESSION["swf"]; ?>">
<param name="quality" value="high">
<embed src="<? echo $_SESSION["swf"]; ?>" quality="high" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash" width="85" height="40"></embed>
</object>
</p>
</body>
</html>