Does your site need to redirect me to the French version (https://faut-il-https-sur-mon-site.fr/) just because I'm in Canada?
No, no it does not.
No, no it does not.
(It's only a naive implementation of parsing the Accept-Language header. Sorry, was all I could do at the time.)
I'm not sure what the standard says, but i suspect you'd surprise users considerably less if you used the first language listed in that header rather than the last (assuming equal or missing q values).
A proper implementation would make for a good Caddy module.
Accept-Language: en-US;q=1.0, en;q=1.0, fr-FR;q=0.5, fr;q=0.5
your website redirects to faut-il-https-sur-mon-site.fr. Turn this off.