Кодировка Quoted-Printable UTF-8 - C#

public static string DecodeEncodedWordValue(string mimeString)
    {
        var regex = new Regex(@"=\?(?<charset>.*?)\?(?<encoding>[qQbB])\?(?<value>.*?)\?=");
        var encodedString = mimeString;
        var decodedString = string.Empty;
     
        while (encodedString.Length > 0)
        {
            var match = regex.Match(encodedString);
            if (match.Success)
            {
                // If the match isn't at the start of the string, copy the initial few chars to the output
                decodedString += encodedString.Substring(0, match.Index);
 
                var charset = match.Groups["charset"].Value;
                var encoding = match.Groups["encoding"].Value.ToUpper();
                var value = match.Groups["value"].Value;
     
                if (encoding.Equals("B"))
                {
                    // Encoded value is Base-64
                    var bytes = Convert.FromBase64String(value);
                    decodedString += Encoding.GetEncoding(charset).GetString(bytes);
                }
                else if (encoding.Equals("Q"))
                {
                    // Encoded value is Quoted-Printable
                    // Parse looking for =XX where XX is hexadecimal
                    var regx = new Regex("(\\=([0-9A-F][0-9A-F]))", RegexOptions.IgnoreCase);
                    decodedString += regx.Replace(value, new MatchEvaluator(delegate(Match m)
                                                                          {
                                                                              byte[] bytes = new byte[m.Value.Length / 3];
 
                                                                              for (int i = 0; i < bytes.Length; i++)
                                                                              {
                                                                                  string hex = m.Value.Substring(i * 3 + 1, 2);
                                                                                  int iHex = Convert.ToInt32(hex, 16);
                                                                                  bytes[i] = Convert.ToByte(iHex);
                                                                              }
                                                                              return Encoding.GetEncoding(charset).GetString(bytes);
                                                                          }));
                    decodedString = decodedString.Replace('_', ' ');
                }
                else
                {
                    // Encoded value not known, return original string
                    // (Match should not be successful in this case, so this code may never get hit)
                    decodedString += encodedString;
                    break;
                }
     
                // Trim off up to and including the match, then we'll loop and try matching again.
                encodedString = encodedString.Substring(match.Index + match.Length + 1);
            }
            else
            {
                // No match, not encoded, return original string
                decodedString += encodedString;
                break;
            }
        }
        return decodedString;
    }