Swap M-x and M-q

Question

How can I swap M-x and M-q?

I can swap C-x and C-q with

;; swap C-q and C-x
(keyboard-translate ?\C-q ?\C-x)
(keyboard-translate ?\C-x ?\C-q)

The following errors out

(keyboard-translate ?\M-q ?\M-x)
(keyboard-translate ?\M-x ?\M-q)

as well as

(keyboard-translate (kbd "M-q") (kbd "M-x"))

I would expect the key references (?\C-x and ?\M-x) to be symmetric, but clearly something in my understanding is off.

EDIT: Reading @phils response and the referenced documentation, I can see that the above fails, at least in part, because there isn't a character in range to translate.

Thinking more about the problem, translation is probably not what I need but rather good old rebinding:

(global-set-key (kbd "M-q") 'execute-extended-command)
(global-set-key (kbd "M-x") 'fill-paragraph)

That is, make M-q call the command which is typically associated with M-x (execute-extended-command) and remap the displaced command (fill-paragraph).

Answer 1

You can use key-translation-map:

(define-key key-translation-map (kbd "M-q") (kbd "M-x"))
(define-key key-translation-map (kbd "M-x") (kbd "M-q"))

Answer 2

A control-modified letter character still results in a character, and hence character translation works for those; but most other modified keys do not result in a character.

(characterp ?\C-q)
t

(characterp ?\M-q)
nil

Both are represented as integers, but there's a limit to the ints which are valid for characterp. See the following for details:

• C-hig (elisp)Character Codes
• C-hig (elisp)Keyboard Events

For translating key sequences generally, see:

C-hig (elisp)Translation Keymaps