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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:
Googlebot sends an "Accept-Language: en" header, meaning it specifies, by default, it accepts English-language webpages. This is inconsistent with the documentation and I think it's new default behavior. It's certainly different than when I last checked when I was involved in this part of Google Search.
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+.
