How can I prevent/override key translation behavior such as: µ (translated from A-m) runs the command self-insert-command

Question

I've bound a command to A-m, however some package that I load seems to modify input translation maps (input-decode-map, local-function-key-map, function-key-map, key-translation-map) that interfere with my intended behavior for the key, which is to run the command I've bound it to. Instead when I press A-m I get:

µ (translated from A-m) runs the command self-insert-command

My questions here are:

1. How can I override this behavior if a package interferes like this?
2. How can I quickly zero-in on which package has interfered in this way without the slow and painful comment-packages/restart emacs cycle?
3. Prevent packages from overriding my custom settings-- or at least warn me when modifying the input maps so I can easily figure out which package without hunting?

Answer 1

This behavior seems to introduced by the packages iso-transl. From the library's commentary (M-xfind-libraryRETiso-translRET)

Loading this package defines three ways of entering the non-ASCII printable characters with codes above 127: the prefix C-x 8, or the Alt key, or a dead accent key. For example, you can enter uppercase A-umlaut as C-x 8 " A' orAlt-" A' (if you have an Alt key) or `umlaut A' (if you have an umlaut/diaeresis key).

To disable the keybinding for A-m introduced by this package add something like this to your init file

(with-eval-after-load 'iso-transl
  (let ((vec (vconcat "m")))
    (aset vec 0 (logior (aref vec 0) ?\A-\^@))
    (define-key key-translation-map vec nil)))

Alternatively if you want to disable all key translation set iso-transl-char-map to nil before iso-transl has loaded. Other way would be map over iso-transl-char-map and unset keys like above, something like this

(dolist (transl-char iso-transl-char-map)
  (let ((vec (vconcat (car transl-char))))
    (aset vec 0 (logior (aref vec 0) ?\A-\^@))
    (define-key key-translation-map vec nil)))

After which your binding for the key will start working. This works, I tested by instructing emacs to use meta key as alt modifier and alt key as meta modifier by doing

(setq x-meta-keysym 'alt)
(setq x-alt-keysym 'meta)

Now M-m will act as A-m, to disable it do the reverse of the above.

I feel you should report this as a bug to emacs-devel, there should be a way to easily disable to the key translations introduced by iso-transl (perhaps there is a way, but I don't see it).