Regular Expressions

bool replacedAny = false;
char[] characters = Texto_Retorno.ToCharArray();
for (int index = 0; index < characters.Length; index++)
{
    switch (characters[index])
    {
        case 'á':
        case 'à':
        case 'ä':
        case 'â':
        {
            characters[index] = 'a';
            replacedAny = true;
            break;
        }
        case 'é':
        case 'è':
        case 'ë':
        case 'ê':
        {
            characters[index] = 'e';
            replacedAny = true;
            break;
        }
        case 'í':
        case 'ì':
        case 'ï':
        case 'î':
        {
            characters[index] = 'i';
            replacedAny = true;
            break;
        }
        case 'ó':
        case 'ò':
        case 'ö':
        case 'ô':
        {
            characters[index] = 'o';
            replacedAny = true;
            break;
        }
        case 'ú':
        case 'ù':
        case 'ü':
        case 'û':
        {
            characters[index] = 'u';
            replacedAny = true;
            break;
        }
    }
}

if (replacedAny)
{
    Texto_Retorno = new string(characters);
}

characters[index] = '3'; // ??

static string RemoveDiacritics(string stIn)
{
    string stFormD = stIn.Normalize(NormalizationForm.FormD);
    StringBuilder sb = new StringBuilder();

    for(int ich = 0; ich < stFormD.Length; ich++) 
    {
        UnicodeCategory uc = CharUnicodeInfo.GetUnicodeCategory(stFormD[ich]);
        if (uc != UnicodeCategory.NonSpacingMark) 
        {
            sb.Append(stFormD[ich]);
        }
    }

    return sb.ToString().Normalize(NormalizationForm.FormC);
}

string input = "Príliš žlutoucký kun úpel dábelské ódy.";
string result = RemoveDiacritics(input); // "Prilis zlutoucky kun upel dabelske ody."

• \abc\rvr\sad\dqwdwq
• \rfdqwdvr\rtgevr\rgwvrr\23rvrv
• \rffewvr\rfewvr\rvfewrr\rvrwefewv

([\\][A-Za-z0-9]+)+