But, just as brainstorming, if I can set an alternative for Alt+F4, what do you think can be a good combination of keys to complement it?
Does the "AltGr" key get much use? Perhaps employ that as the "shift" key, with Pete2's suggestion of "Q" (for "quit", I assume).
IIRC, the IBM PC keyboard sends a mix of signals to the OS: printable symbols (abc 0123 &c) go as a key number which is translated into the actual symbol code according to the currently configured national keyboard; but shift keys go as status bits alongside key numbers.
So the keyboard always should send the full set of shift key information, no? The IBM 101-keyboard (as in USian m/cs) is extended in the UK to 102 keys (for GBP/£ sign), which would call for a key number that in the 101-kbd is not available. Whether those oddball kbds ensure a given symbol key sends the right key number, I dunno -- there's a lot of tomfoolery going on in the world of computing these days, IMHO.
If I got any of that wrong, would some kind soul set me straight? Ta.