WorldIP - free geolocation database, service and tools

Opera browser users are able to go online through a special proxy server of the Opera. Also, Opera Mini mobile customers use these servers.

Of course, IP addresses belong to these servers, but they send header "X-Forwarded-For" with the real IP address of the user.

The list of Opera's proxies is helpful to determine the real country.

Opera runs data centers in Norway, Iceland, Poland, USA and China.

Include file of proxies, then nginx automatically takes the real IP address, to determine the real country of the visitor.

You can download always actual database of Opera's proxies here:
http://wipmania.com/static/worldip.opera.conf

Use in nginx:

geo $country {
 default XX;
 include /etc/nginx/conf/worldip.opera.conf;
 include /etc/nginx/conf/worldip.conf;
}