Reproduce a SAIL code similar to the one below.

On ActiveUnitChanged(un) do begin

   if un = G01 and GetNation(un) = nation_russian then begin
      PlaySoundXY(GetX(un),GetY(un),'01_1i-Off1-1'); end;
   end;

Try triggering this event in-game by clicking on the character.

This won't work if you do it from the User interface. You have to click on the unit on the terrain directly.

Unit HAS to be a human that is placed on the terrain. Also the last active unit saved doesn't change if you click on vehicles or buildings.