addHelpButton can only be used to serve language string that do not receive any argument because there is no argument forwarded to help_icon.

I'm not sure if this is due to any technical limitation, but it would be something nice to do as help contents can depend on different stuff.

The use case I have is a selector with a list of elements, 3rd party plugins can add extra elements to the selector, so it is not enough to hardcode core elements in the help text.