Complex “Contains” string comparison

You could use an appropriate CompareInfo and then CompareInfo.IndexOf(string, string, CompareOptions) and check the result against -1. Sample:

using System;
using System.Globalization;

class Program
{
    static void Main()
    {
        var compareInfo = CultureInfo.InvariantCulture.CompareInfo;
        var options = CompareOptions.IgnoreCase | 
            CompareOptions.IgnoreSymbols |
            CompareOptions.IgnoreNonSpace;

        var haystack = "bla Lé OnAr d/o bla";
        var needle = "leonardo";

        var index = compareInfo.IndexOf(haystack, needle, options);
        Console.WriteLine(index); // 4
    }
}

Or in method form:

private static bool ComplexContains(string source, string value)
{
    var index = CultureInfo.InvariantCulture.CompareInfo.IndexOf
        (source, value, CompareOptions.IgnoreCase | 
         CompareOptions.IgnoreSymbols | CompareOptions.IgnoreNonSpace);
    return index != -1;
}