Google sort of respects the header, but my experience has been that the behavior is odd.
I was working on adding localization to a web site, and so changed my headers to prefer Japanese. I accidentally left this on when I visited AdWords. I put English back to the top, but it took a week or so of manually changing the interface back to English for it to stick. Took one time to get it in Japanese, and about 50 to get it back to English.
I was working on adding localization to a web site, and so changed my headers to prefer Japanese. I accidentally left this on when I visited AdWords. I put English back to the top, but it took a week or so of manually changing the interface back to English for it to stick. Took one time to get it in Japanese, and about 50 to get it back to English.