[lazide]

Having been involving in some internal projects and done the data analysis (not in Search, other areas), your guess is correct - far more people get (clearly) wrong results if you serve what the browser is asking for due to mis configuration. It’s easy to tell due to differences in various conversion metrics and huge increases in clicks to language change buttons.

It drove me crazy too before I saw the data. Geo-IP, while not awesome for exactly the scenario you are describing, is more predictable since it gives a set of baseline language/settings that are ‘right’ based on norms in the area, and people know how to navigate out of generally if they’re not the ‘baseline’ user there. (An English speaker in Japan pretty quickly needs to know how to switch languages or learn Japanese or they aren’t going to be able to even navigate the subway/buy tickets for instance!)

Many of the browser based settings get people stuck, especially since most large websites do the same geoip thing now.

It does make it awkward for folks not doing ‘the norm’ in their area, or who have an IP improperly categorized, but statistically they aren’t as common and they figure out how to handle it usually.