PHP Locale获取国家/地区代码

I am currently getting a user's country in PHP using the following method;

Locale::getDisplayRegion($_SERVER[HTTP_ACCEPT_LANGUAGE],'en')

This returns the countries name in text e.g. United States.

However, I want to return the abbreviated country code from the $_SERVER[HTTP_ACCEPT_LANGUAGE] request rather than the full text name. How can I do this?

The Symfony framework has a handy function for determining the preferred language based on the Accept-Language header:

https://github.com/symfony/HttpFoundation/blob/master/Request.php#L1463
https://github.com/symfony/HttpFoundation/blob/master/Request.php#L1498