C#: Replace random letters with letters from another keyboard layout

Question

Sorry for my bad english. So, i have a code.

    public Random rnd = new Random();

    public string RandomizeLetters(string text)
    {
        string variations = "";

        foreach (var letter in text)
        {
            var а = new List<string> { "а", "аa" };
            var е = new List<string> { "е", "еe" };
            var о = new List<string> { "о", "оo" };
            var р = new List<string> { "р", "рp" };
            var с = new List<string> { "с", "сc" };
            var у = new List<string> { "у", "уy" };
            var х = new List<string> { "х", "хx" };

            var alphavite = new List<List<string>> { а, е, о, р, с, у, х };

            var res = new StringBuilder();

            foreach (var x in alphavite)
            {
                if (x.Exists(e => e.EndsWith(letter.ToString())))
                {
                    res.Append(x[1][rnd.Next(0, x[1].Length)]);
                }
            }

            res.Append(letter.ToString());

            variations += res;
        }

        return variations.ToString();
    }

This code replaces random letters with letters that are visually similar to letters from a different keyboard layout, in my case, from Russian keyboard layout to the English keyboard layout. But instead of the desired result, I get text with duplicate characters.

Here is the text I want to process:

Для проверки наличия в вашем тексте символов из другого языка - скопируйте исходный текст, вставьте его в поле ниже, и выберите нужный чекбокс языка

But the text that I get at the output:

Для пpроовeеpрки нaаличия в ваашeем теекcстeе cсимвоолоов из дрруугоогоо языкaа - сскоопиpрууйтее иcсxхoодный теекcст, всстaавьтее eегoо в поолeе нижее, и выбeеpритeе нyужный чеекбоокcс языкаа

How to fix it? I check the text with the help of the service for checking the characters: raskladka.obmen-service.com

Answer 1

Even if you replace letter with res.Append(x[1][rnd.Next(0, x[1].Length)]); later you still append base letter: res.Append(letter.ToString()); Try adding a condition:

        bool replaced = false;
        foreach (var x in alphavite)
        {
            if (x.Exists(e => e.EndsWith(letter.ToString())))
            {
                res.Append(x[1][rnd.Next(0, x[1].Length)]);
                replaced = true;
            }
        }
        if(!replaced)
            res.Append(letter.ToString());