> Is this to avoid breaking lines where they shouldn't be?  If so, we
> already have fill-french-nobreak-p; see fill.el.
>

Thanks, I didn't know that.


> If this is for some other purpose, i.e. if typing French text needs to
> insert no-break-space character for a purpose other than filling the
> text correctly, then would someone please explain the needs, before
> presenting solutions?
>

French text typed in Emacs is not necessary rendered in Emacs only: An HTML
page written in Emacs but rendered in Firefox will have it's line breaks at
different places and non-breaking spaces will apply for Firefox as well as
Emacs.

Other example: I use to type text in Emacs and later copy-paste in word
processing applications; I am happy to have non-breaking spaces already in
place.
-- 
Matthias