Should a toggle button show its current state or the state to which it will change?
(ux.stackexchange.com)
In my opinion, any button in terms of graphical UI design simply dispatches an action with no arguments regarding state. There doesn't exist a dichotomy between a "toggle" mechanic and a "standard" button as far as the button itself is concerned.
Whether or not you want to update the visual representation of that button is a separate concern.