RemoveDiacritics.cs

public static string RemoveDiacritics(this string str) {
  var formD = str.Normalize(NormalizationForm.FormD);

  var bp = 0;
  var buffer = new char[formD.Length];
  for(var i = 0; i < formD.Length; i++)
    if(UnicodeCategory.NonSpacingMark != CharUnicodeInfo.GetUnicodeCategory(formD[i]))
      buffer[bp++] = formD[i];

  return new string(buffer, 0, bp);
}