emacs/flyspell

M-x flyspell-buffer

Starting new Ispell process aspell with default dictionary...
ispell-init-process: Erreur : No word lists can be found for the language "fr_FR".

cat /usr/lib/ispell/README.select-ispell

Please use 'select-default-ispell' superuser script
to change your selection.

Note that you will need to run that script and select
the 'manual' option if you want to play with symlinks
yourself.

apt install aspell-fr