Hi,
I have success using formbuilder with qtranslate.
I just modified a line code in formbuilder.php on line 568:
This one:
$form['action_target'] = $_SERVER['REQUEST_URI']. "#$formCSSID";
To this:
$form['action_target'] = $GLOBALS['HTTP_SERVER_VARS']['REQUEST_URI'] . "#$formCSSID";
You can read about this issue here: https://ckon.wordpress.com/2006/08/09/server-request_uri-doesnt-always-work-correctly-heres-how-to-fix/
I think this could help other plug-ins and forms with submission witch use $_SERVER[‘REQUEST_URI’] in conjunction with qtranslate.
Good luck!