The buttons on each side of the device correspond with the flags displayed on the screen.
The button you press is the language you speak in. The opposite button is the language that your words will be translated into.
For instance, Travis displays a Dutch flag on the right side of the screen and a French flag on the left.
Press the right button (circle) once to speak in Dutch and translate into French, and vice-versa. After pressing a button, wait for the beeping sound before speaking.