When you land on the page, it defaults to Icelandic (it did from me and I'm from Canada): https://island.is/forsetaframbod

However, it does have an "EN" button near the top right. Personally, I think this is as close to a perfect solution as you can get. (Geolocating an IP or something has a whole bunch of problems than just going with your country's official language as a default.)