I finally found out how to use this app properly! This is what I did : I have a French AZERTY layout on the keyboard, but on the "Physical Keyboard" section of my settings, I chose the English (US) layout (don't ask my why I this works, I don't know...). And then, I chose the French layout for this Belkin Keyboard Extention and it worked! Problem solved :)
I have the F5L170 keyboard. This app gives the wrong keys for various signs such as the @ and the pound sign. Neither of the other two Belkin character apps, which claim to fix bugs, solve this problem.
Added compatibility for the Mobile Wireless Keyboard (F5L175)