Good question; one person is annoyed by this endlessly a few offices down from me. It's hard to make sure that things are handled consistently sometimes, but if you use google.com/ncr or the "Google.com in English" link at the bottom of the home page, that should help. The "Language tools" link to the right of the search box should also let you set a cookie with your language preference.

And yet for some reason, the search link from Google Toolbar seemed to ignore that cookie and certainly ignored my account preferences, sending me to the localized search page regardless.

Short version of long story: I used to bounce my net traffic through an ssh tunnel to a hosted VM. The VM was moved to a new machine in south-east asia. Having Google Toolbar constantly send my searches to the localized engine, despite the cookie selection, my being logged in and my preferences being clearly set, was more of a day-to-day annoyance than having my traffic piped across the Pacific twice.

I appreciate that you went and asked someone for the clarification that this issue is about the preference being set in a cookie and not in user settings, but this doesn't solve the problem for many of us.

For YEARS, on a weekly and sometimes daily basis, always logged-in, always with preferences set to english, it is infuriating to routinely end up receiving results that conflict with your explicit language settings.

What, concretely, do we have to do to get someone at google to push a change from using cookies to a real user-setting to fix this absurdity?

You said they did it for speed. Giving me completely incorrect results in a language I can't even read 1 millisecond faster than giving me results that I actually care about is a win? This is over-optimization.

Exactly, and it's cross-device, cross-service. What about browser built-in search? Or mobile? Or not wanting cookies or having to log in? I see my browser having a preferred language setting...