How are your buttons set up? I don't know anything about the button class, but
if your buttons are movieclips, then it would be easy to setup an array of four
booleans. When you create the button, give it an onRelease (or on Press)
function of turning its respective boolean in the array to "true."

try this:

http://furatena.com/german/button.swf
http://furatena.com/german/button.fla