I think a good way to do this would be to set a new session variable that will hold this checkout success page value. If your language id is held in a session variable called language id then the code to set this session variable for the checkout success page should look something like this:
$_SESSION['checkout_success'] = "checkout_success_" . $_SESSION['language_id'] . ".php";
You would then also need to have an if statement after the checkout page that will check the country if the language id is 1 and set the variable accordingly. In order for this to work you must have a session variable set to hold the selected country.
if($_SESSION['language_id'] == '1' && $_SESSION['country'] == 'Germany'){
$_SESSION['checkout_success'] = "checkout_success_5.php";
}
When you configure the Store Order Summary or another server behavior that is the last to occur on the confirm page then you should specify this session variable as the redirect page like this:
<?php echo $_SESSION['checkout_success'] ?>
I think this should get you the result you are looking for. Remember that you will still need to set the session variable to hold the selected country, you can use the standard eCart set session value server behavior for that.
