How to convert JSON to AppleScript properties
The easiest way is to use JSON Helper app available on the AppStore. Then you simply do something like this:

tell application "JSON Helper"
    set json to fetch JSON from "http://ip-api.com/json/8.8.8.8?fields=country,city,isp,org,as,mobile,proxy,message"
    set countryName to |country| of json
end tell


Result: "United States"