I hooked up 3 extra usb keyboards, ran a separate translate for each one:

Code
sudo ./translate /dev/input/by-id/usb-0461_USB_Wired_Keyboard-event-kbd &
sudo ./translate /dev/input/by-id/usb-USB_USB_Keyboard-event-kbd &
sudo ./translate /dev/input/by-id/usb-Microsoft_Wired_Keyboard_600-event-kbd &

[Linked Image from i.imgur.com]

Pressing keys on each keyboard simultaneously in jstest-gtk.