title: REST API request with language and region
body: <p>I'm developing a REST API and I need to implement a method which needs language and country to produce result in the correct format since the result contains numbers and dates.</p>
  
  <p>I was using the HTTP <code>Accept-Language</code> header to get the language. The specs define the header as a language specifier, but now I'm not sure if it is correct to use this header for getting the country. For example, I want to allow a result in Spanish language but with numbers in English format (with commas instead of dots). </p>
  
  <p>Is <code>es-US</code> an accepted value for the <code>Accept-Language</code> header?</p>
  
  <p>I was thinking that I could develop a new custom header like <code>X-Country</code> for my REST API.</p>
  
  <p>Any thoughts? Thanks.</p>