Add an event on the RadVirtualKeyboard class that is raised when a key button is pressed. For example, KeyPressed or something like this. 

Hook to external keyboard special keys degrades performance the control so it might be useful to provide an API to disable this functionality.

On English keyboard the AltGr key is treated as Right Alt key which behaves the same as the standard (Left) Alt key. However, on some cultures (like French) the AltGr key is used as a modifier that toggles few special keys. This behavior is similar to holding the Shift key, but the set of special keys that are activated is different.

Currently, RadVirtualKeyboard doesn't support the special behavior of the AltGr key.