Convert a Unicode string to an escaped ASCII string

Question

How can I convert this string:

This string contains the Unicode character Pi(π)

into an escaped A

Answer 1

A small patch to @Adam Sills's answer which solves FormatException on cases where the input string like "c:\u00ab\otherdirectory\" plus RegexOptions.Compiled makes the Regex compilation much faster:

    private static Regex DECODING_REGEX = new Regex(@"\\u(?[a-fA-F0-9]{4})", RegexOptions.Compiled);
    private const string PLACEHOLDER = @"#!#";
    public static string DecodeEncodedNonAsciiCharacters(this string value)
    {
        return DECODING_REGEX.Replace(
            value.Replace(@"\\", PLACEHOLDER),
            m => { 
                return ((char)int.Parse(m.Groups["Value"].Value, NumberStyles.HexNumber)).ToString(); })
            .Replace(PLACEHOLDER, @"\\");
    }