UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/604.5.6 (KHTML, like Gecko) Version/11.0.3 Safari/604.5.6

Steps to reproduce the problem:
1. Run Chromium in headless mode
2. Navigate to http://localhost:9222 in non-headless browser and click to 'about:blank' link
3. In opened app enter any valid url
4. Observer the Network tab and check the first request to the domain.

What is the expected behavior?
Accept-Language header must be presented in the HTTP headers

What went wrong?
Accept-Language header is missing from HTTP headers

Did this work before? No 

Does this work in other browsers? Yes

Chrome version: 66.0.3342.0  Channel: canary
OS Version: OS X 10.12.6
Flash Version: 

Headfull version of Chromium uses OS and Browser preferences to set the Accept-Language header. Since we can't do it in Headless version, can we set it from command line?