How to replace special characters with their equivalent (such as " á " for " a") in C#?

You could try something like

var decomposed = "áéö".Normalize(NormalizationForm.FormD);
var filtered = decomposed.Where(c => char.GetUnicodeCategory(c) != UnicodeCategory.NonSpacingMark);
var newString = new String(filtered.ToArray());

This decomposes accents from the text, filters them and creates a new string. Combining diacritics are in the Non spacing mark unicode category.

string text = {text to replace characters in};

Dictionary<char, char> replacements = new Dictionary<char, char>();

// add your characters to the replacements dictionary, 
// key: char to replace
// value: replacement char

replacements.Add('ç', 'c');
...

System.Text.StringBuilder replaced = new System.Text.StringBuilder();
for (int i = 0; i < text.Length; i++)
{
    char character = text[i];
    if (replacements.ContainsKey(character))
    {
        replaced.Append(replacements[character]);
    }
    else
    {
        replaced.Append(character);
    }
}

// 'replaced' is now your converted text

For future reference, this is exactly what I ended up with:

temp = stringToConvert.Normalize(NormalizationForm.FormD);
            IEnumerable<char> filtered = temp;
            filtered = filtered.Where(c => char.GetUnicodeCategory(c) != System.Globalization.UnicodeCategory.NonSpacingMark);
            final = new string(filtered.ToArray());