Read JSON as a dictionary of country codes and names
There's nothing wrong with what you currently have. However, a plist is another option, if this JSON is just static file.

The nice thing about the property list format is that Xcode has built-in support for editing it and Foundation has built-in support for reading it. 

fileprivate func loadNames() {
    if let filePath = Bundle.main.path(forResource: "countryNames", ofType: "plist") {
        countryNames = NSDictionary(contentsOfFile: filePath)!
    }
}