Who An English Browser on a New Zealand Connection ?

We are testing a multilingual website through New Zealand proxies, and someone expected the IP address to control every regional setting. The site still opens in French because that language was selected during an earlier visit. This has turned into an argument about whether the proxy is working. I think we are confusing network location with saved preferences, but I need a clear way to demonstrate it. How would you test which signal the website follows without assuming that every visitor in New Zealand uses English or wants the same regional content?