This problem, in EU we use decimal-comma instead of decimal-point, is partly solved in this thread.
http://www.zen-cart.com/forum/showthread.php?t=75999

It works in the checkout process, but the problem still exists in de GV-send option.

The earlier thread is closed without a solution for GV-send
Anybody figured it out yet?

Definitely to complex for me. I just think this file is involved.

includes/modules/pages/gv_send/header_php.php