difference between get_header() or include(TEMPLATEPATH . ‘/header.php’)?

Is there any difference using
get_header()
or
include(TEMPLATEPATH . ‘/header.php’)?

I want to use a redirection to the good header.php page depending on the browser language using:

<?php
if (!isset($langue_user) && !isset($_SESSION["ch_langue"])){
$langue_user=substr($_SERVER["HTTP_ACCEPT_LANGUAGE"], 0, 2);
	switch($langue_user){	

	case "en":
	$_SESSION["ch_langue"] = "en";
	break;

	default:
	$_SESSION["ch_langue"] = "fr";
	break;
	}
}
?>

Any advice to do that properly?