title: What information do browsers use to create the Accept-Language string?
body: <p>I'm trying to get as much regional information as possible about users visiting a website. Mapping the IP to a country using e.g. ipinfo.io is one method, but I'm also exploring the Accept-Language header. Getting this using HTTP_ACCEPT_LANGUAGE in PHP. I would like to ask if someone knows how this is actually computed? I understand that it is up to the browser, and the implementation is different depending on browser, but is there some documentation available or interesting article written on this?</p>
  
  <p>I'm using Linux, my operation system language is English, and I have a Swedish keyboard layout. For Chrome I see this string:</p>
  
  <pre><code>en-US,en;q=0.8,nl;q=0.6,sv;q=0.4
  </code></pre>
  
  <p>Which indicates that I'm interested in English and Swedish, which makes sense, but then there is also Dutch there, where might this have come from?</p>
  
  <p>For Firefox I only see:</p>
  
  <pre><code>en-US,en;q=0.5
  </code></pre>
  
  <p>Anyone who has done some more research on this? Any other tips or comments regarding how to get regional information about visitors of websites?</p>
  
  <p>Thanks!</p>