Former Googler, Pierre Far, spotted and posted on Google+ that the Google crawler (GoogleBot) now sends HTTP requests with English setting Accept-Language in the request header. He notes that the documentation specifically says GoogleBot doesn’t specify a language in the request header for the Accept-Language, it says it sends it “without.”

Pierre wrote:

It seems the proper people are notified about the documentation error and either it is a bug with GoogleBot or a bug in the documentation, but it is important to note for those who do international webmastering/SEO.

Forum discussion at Google+.