1.) You cannot just put no supported language (NA language) in the http header. A website needs to know in what language to render otherwise it will break websites for 99% users.
Appropriate thing is to put your language to En-US both at browser and OS level. And not to add other language packs (secondary language installed)
2.) Timezone is also important for webpages to render. Eg, whatsapp messages.
Right now, brave (chromium) timezone is picked from the OS instead of internal directory unlike firefox RFP.
So, to change your timezone (either setup as GMT or randomize it) it needs to manually on OS level. On Linux, you can change OS timezone to GMT and then add a widget to show your actual regional timezone.
timedatectl
sudo timedatectl set-timezone UTC
3.) Font and Language fingerprinting is already improved quite lot in brave https://brave.com/privacy-updates/17-language-fingerprinting/
4.) https://github.com/brave/brave-browser/issues/11770
V1 and v2 are already done