Reference of how pig latin translator works

private void Form1_Load(object sender, EventArgs e)
        {
            string ToPigLatin(string sentence)
            {

                const string vowels = "AEIOUaeio";
                List<string> pigWords = new List<string>();

                foreach (string word in sentence.Split(' '))
                {
                    string firstLetter = word.Substring(0, 1);
                    string restOfWord = word.Substring(1, word.Length - 1);
                    int currentLetter = vowels.IndexOf(firstLetter);

                    if (currentLetter == -1)
                    {
                        pigWords.Add(restOfWord + firstLetter + "ay");
                    }
                    else
                    {
                        pigWords.Add(word + "way");
                    }
                }
                return string.Join(" ", pigWords);
            }

           Console.WriteLine(ToPigLatin("this is a test sentence to see if pig latin actually works and what will become of this"));
        }