adding template and lang to login form

[jnet]

INTEGRATION CODE

we have
Clients Login - Add this code to a page on your site to display a clients login form to log clients into the WHMCS Client Area................................

How can I add template and language to the red part?

<form method="post" action="http://mydomain.com/clients/dologin.php?goto=clientarea">
Email Address: <input type="text" name="username" size="50"><br>
Password: <input type="password" name="password" size="20"><br>
<input type="submit" value="Login">
</form>

[Nick]

Add:
&systemtemplate=templatename

To the end of:
http://mydomain.com/clients/dologin.php?goto=clientarea

To specify the template to display. I'm not sure if changing language is possibly by the URL, but it is via the selection box at the bottom of the page.