Actually, Google goes by the Accept-Language header; for me it seems to do so, anyway. My browser is set to ask for English pages, and consequently I stay on google.com, even though I'm in Germany, where you're usually redirected to google.de.
Actually, Google goes by the Accept-Language header
Hmmm... didn't seem to work for me. I was using my linux laptop, dialing in to ATT Global in Geneva. The language setting for my Mozilla config on the laptop is English.