If you're not testing any low level network stuff.
You can possibly break this down into 2 separate problem.
1) The impact of the network latency of fetching the data/content from different locations.
2) The performance difference in rendering localized content.
You can use global proxies to do measurements for 1. Then use a local debugging proxy like Charles and Wireshark to as it to introduce latency to match the desired country, to do more tests locally.
For the 2nd one, you can work with your developers to see how they determine which content to serve, and use some method of faking your location. I'd probably would recommend the developers have some sort of hook where you can pass in some sort of secret parameter to switch your locale. ?locale=enUS or something.