In testing headless chrome I have noticed that it does not transmit the Accept-Language header entry. I have confirmed that it does get sent when there is a visible browser window.
Is there a reason for this and does chrome have an option to require/force it to send these normal values?
To see this, you can fire up Fiddler and type this at the command line:
chrome --headless --incognito --window-size=1920,1080 --disable-gpu --no-sandbox http://www.daringfireball.net/
In the Fiddler inspector (raw view) you'll see this:
GET https://daringfireball.net/css/ie_sucks HTTP/1.1
Host: daringfireball.net
Connection: keep-alive
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/65.0.3325.181 Safari/537.36
Accept: text/css,*/*;q=0.1
Referer: https://daringfireball.net/
Accept-Encoding: gzip, deflate
Whereas running the same command without --headless gives you this:
GET https://daringfireball.net/css/ie_sucks.php HTTP/1.1
Host: daringfireball.net
Connection: keep-alive
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36
Accept: text/css,*/*;q=0.1
Referer: https://daringfireball.net/
Accept-Encoding: gzip, deflate, br
Accept-Language: en-GB,en-US;q=0.9,en;q=0.8
It would appear that Accept-Language is a user-profile header sent only when the browser has a confirmed user specifying a language and as headless has no user it can/does not send that header. This was raised in these posts and looks to be a lacking feature for the foreseeable future:
https://github.com/SeleniumHQ/selenium/issues/4437 https://bugs.chromium.org/p/chromedriver/issues/detail?id=1925