Bug: negotiateLocale bug in Safari with fr-ca locale

[includebeer]

I have set the parameter negotiateLocale = true in app/Config/app.php
The problem is request->getLocale() doesn't always return the right locale.

In Chrome the language is set to french first, then english, and it's working as expected, getLocale return "fr":

request->getUserAgent() = Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.149 Safari/537.36
request->getHeaderLine('accept-language') = fr-FR,fr;q=0.9,en-US;q=0.8,en;q=0.7
request->getLocale()                      = fr

But in Safari, it's only set to french and getLocale return "en":

request->getUserAgent() = Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_3) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.0.5 Safari/605.1.15
request->getHeaderLine('accept-language') = fr-ca
request->getLocale()                      = en

This is on macOS 13.15.3 (Catalina) with CodeIgniter 4.0.2, PHP 7.4.2.
The supported languages are set to ['en', 'fr'].

My guess is there's a bug in the class Negotiate when parsing the accept-language header. The expected behavior would be that getLocale() return "fr" when accept-language is set to "fr-ca". But it looks like it doesn't recognize "fr-ca" as valid, and fall back to "en".