Simple helper to find and convert RegionInfo details using two or three letter Country Codes

RegionInfoFinder.cs

using System;
using System.Globalization;
using System.Linq;

namespace CajunCoding
{
    /// <summary>
    /// Simple helper to find and convert RegionInfo details using two or three letter Country Codes.
    /// NOTE: Inspired but fully rewritten from the Gist: https://gist.github.com/BenjaminAdams/277928c7ad291ea7aea8
    /// </summary>
    public static class RegionInfoFinder
    {
    public static class RegionInfoFinder
    {
        private static readonly ILookup<string, RegionInfo> RegionInfoLookupByThreeLetterCountryCode = CultureInfo
            .GetCultures(CultureTypes.SpecificCultures)
            .Select(c => new RegionInfo(c.Name))
            .ToLookup(ri => ri.ThreeLetterISORegionName, StringComparer.OrdinalIgnoreCase);

        private static readonly ILookup<string, RegionInfo> RegionInfoLookupByTwoLetterCountryCode = CultureInfo
            .GetCultures(CultureTypes.SpecificCultures)
            .Select(c => new RegionInfo(c.Name))
            .ToLookup(ri => ri.TwoLetterISORegionName, StringComparer.OrdinalIgnoreCase);

        public static RegionInfo? FromThreeLetterCountryCode(string threeLetterCountryCode)
            => RegionInfoLookupByThreeLetterCountryCode[threeLetterCountryCode].FirstOrDefault();

        public static RegionInfo? FromTwoLetterCountryCode(string twoLetterCountryCode)
            => RegionInfoLookupByTwoLetterCountryCode[twoLetterCountryCode].FirstOrDefault();
    }
    }
}

Inspired by the original gist here: https://gist.github.com/BenjaminAdams/277928c7ad291ea7aea8 but incorporates the fix noted in one of the comments and streamlines the logic with Linq and faster lookup caching...