using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var listExample = new List<string>(){ "banana", "apple", "lemon", "orange",

            "cherry", "pear", "яблоко", "лимон", "груша", "банан", "апельсин", "вишня" };

        var result = listExample.OrderByCyrillicFirst();

        foreach(var item in result)

        {

            Console.WriteLine(item);

        }

        Console.WriteLine();

        var resultDescending = listExample.OrderByCyrillicFirstDescending();

        foreach(var item in resultDescending)

        {

            Console.WriteLine(item);

        }

    }

}

​

​

public static class MyExtensions

{

     public static IEnumerable<string> OrderByCyrillicFirst(this IEnumerable<string> list)

     {

         var cyrillicOrderedList = list.Where(l => string.IsNullOrEmpty(l) ? false : IsCyrillic(l[0])).OrderBy(l => l);

         var latinOrderedList = list.Where(l => string.IsNullOrEmpty(l) ? true : !IsCyrillic(l[0])).OrderBy(l => l);

         return cyrillicOrderedList.Concat(latinOrderedList);

     }

​

     public static IEnumerable<string> OrderByCyrillicFirstDescending(this IEnumerable<string> list)

     {

         var cyrillicOrderedList = list.Where(l => string.IsNullOrEmpty(l) ? false : IsCyrillic(l[0])).OrderByDescending(l => l);

         var latinOrderedList = list.Where(l => string.IsNullOrEmpty(l) ? true : !IsCyrillic(l[0])).OrderByDescending(l => l);

         return cyrillicOrderedList.Concat(latinOrderedList);

     }

​

    private static bool IsCyrillic(char ch)

    { 

        return ch >= 1024 && ch <= 1273;

    }

}