Pour Emacs, ajouter dans le .emacs
(global-set-key [f31] '(lambda () (interactive) (insert "ch")))
(global-set-key [S-f32] '(lambda () (interactive) (insert "CH")))
(global-set-key [f33] '(lambda () (interactive) (insert "c'h")))
(global-set-key [S-f34] '(lambda () (interactive) (insert "C'H")))
(global-set-key [f35] '(lambda () (interactive) (insert "C'h")))

Pour xterm, ajouter dans .Xdefaults ou .Xresources ou equivalent
*VT100.Translations: #override \
Shift<Key>F31: string("CH")\n\
<Key>F31:      string("ch")\n\
Shift<Key>F33: string("C'H")\n\
Meta<Key>F33:  string("C'h")\n\
<Key>F33:      string("c'h")\n