Generator for mapping national alphabets to the Basic Latin

GenerateBasicLatinMapping.cs

           var unidecodeLines = File.ReadAllLines(@"C:\Users\username\Desktop\Unidecode\unidecode.tsv");
            var outputFile = @"C:\Users\username\Desktop\Unidecode\onlyletters.tsv";

            Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
            var encodings = new[] {
                10000, 10006, 10007, 10010, 10017, 10029, 10079, 10081, 10082,
                1250, 1251, 1252, 1253, 1254, 1257, 1258
            }.Select(i => Encoding.GetEncoding(i)).ToArray();
            bool isSupportedEncoding(string s)
                => encodings.Any(e => e.GetString(e.GetBytes(s)) == s);

            // Hangul consonant and vowels: 매니저 -> ᄆ ᅢ ᄂ ᅵ ᄌ ᅥ -> MAeNIJEo (manager)
            //HashSet<char> jamos = Enumerable
            //    .Range(0xAC00, 0xD7B0 - 0xAC00)
            //    .SelectMany(ch => ((char)ch).ToString().Normalize(NormalizationForm.FormKD))
            //    .Where(ch => ch < 0xD000)
            //    .ToHashSet();

            var latinRegex = new Regex(@"^[a-z]+$");
            var letterRegex = new Regex(@"\p{L}");
            var map = new Dictionary<string, string>();

            var originalMap = new List<(string Key, string Value)>();
            foreach (var line in unidecodeLines)
            {
                var values = line.Split('\t');
                if (values.Length >= 2)
                {
                    var key = values[0];
                    var value = values[1].Trim('\'');
                    originalMap.Add((key, value));
                }
            }

            foreach (var (key, value) in originalMap
                .OrderBy(_ => _.Key.Normalize(NormalizationForm.FormKD) != _.Key)
                .ThenBy(_ => _.Key))
            {
                var decKey = key.Normalize(NormalizationForm.FormKD);
                if (decKey != key)
                {
                    decKey = decKey[..1];
                    if (decKey == value ||
                        map.TryGetValue(decKey, out var decValue) && value == decValue)
                    {
                        continue;
                    }
                }

                if (key.Length == 1 &&
                    letterRegex.IsMatch(key) &&
                    isSupportedEncoding(key) &&
                    latinRegex.IsMatch(value))
                {
                    map[key] = value;
                }
            }
            var res = map
                .GroupBy(pair => pair.Value, pair => pair.Key)
                .OrderBy(g => g.Key)
                .Select(g => g.Key.ToUpperInvariant() + string.Join("", g.OrderBy(s => s)));

            File.WriteAllText(outputFile, string.Join("", res));