As a note, I found a computer with ALTGR to look at and Windows treats ALTGR as a right ALT. I can use it just like I'd use the left ALT. For example, I can ALTGR-Left to go back in a browser or ALTGR-Right to go forward. I'm not sure if the function of the key is changed based on the Windows locale or the keyboard layout chosen or what. But it appears that Windows does allow ALTGR to function as a normal ALT key in certain circumstances. Making mIRC treat the right ALT as ALTGR no matter what doesn't even follow how Windows handles that key, so it would be better to not force it in mIRC.