using System;

using System.Linq;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var s = "jüri-péter o'käärkäsi éter";

        var regex = new Regex(@"[\p{Z}\p{P}]+");

​

        Console.WriteLine(s);

        regex.Split(s).ToList().ForEach(w => s = s.Replace(w, w.ToFirstCap()));

        Console.WriteLine(Environment.NewLine + s);

    }

}

​

public static class StringExtensions

{

​

    public static string ToFirstCap(this string s)

    {

        if (string.IsNullOrEmpty(s))

        {

            return string.Empty;

        }

        return char.ToUpper(s[0]) + s.Substring(1).ToLower();

    }

}