There is still a variety of valid use cases and design though, no? Say your site offers English, Chinese, Japanese, and a number of other languages. Your user'

There is still a variety of valid use cases and design though, no? Say your site offers English, Chinese, Japanese, and a number of other languages. Your user's HTTP header says they can accept Japanese. So you default to Japanese. Their IP says they're in China. Wouldn't you want Chinese to be the 2nd choice on the language list to choose from, because that's a more likely choice for the user (if they were to have to switch) rather than English, French, Spanish, etc.? I'm sure it doesn't take a lot of imagination to think of a lot of other use cases. At the end of the day, it just gives you one more data point to act on. ;)