If you're in a region that google defaults to another language, &hl=en (or another language code) is very useful. Nowadays I mainly use it for the maps site, but I've used it elsewhere before when I couldn't struggle through a website in another language. It's very hard to get it into certain google products, like recaptcha. So I have to learn the words for what it wants clicked.

I don't know if parsing the Accept-Language header is too slow, or if google's trying to encourage people to log in to an account.

Are these params documented, or just reverse engineered from the JS or something? TFA didn't cite its source, either

But verbatim is not useful these days imo. Usually I rather accept that there doesn't exist such information than waste time in googling stuff.