The Active Language via Browser section of Learn GRAV https://learn.getgrav.org/content/multi-language#active-language-via-browser explains that a language of a web page could be selected by the Accept-Language header of http. But this requires to support any variant of this header by corresponding pages. Example: one must create page variants for English in UK: en-GB, in the US: en-US, in Australia en-AU. This comes from installing browsers on devices with local settings.
A great GRAV feature would be to trim this down: if en-US is in Accept-Language then check first if there is an en-US page, if not test if there is an en page, if not show the default language.
That’s a great idea. Best chance of it happening is to create an issue so the team doesn’t lose track of it.