LanguageAutoDetect

    public static class LanguageAutoDetect
    {

        private static int GetCount(string text, params string[] words)
        {
            var commonWordSet = new HashSet<string>(words);
            var boundaryCharsSet = new HashSet<char>
            {
                '.', ' ', '}', ']', ')', '(', '[', '{', '-', '|', '?', '!', '&', '\r', '\n', ',' ,':', '>', '<','\'', '"'
            };

            int len = text.Length;
            int l = 0;
            var count = 0;
            for (int r = 0; r < len; r++)
            {
                if (char.IsLetter(text[r]) && !char.IsLetter(text[l]))
                {
                    l = r;
                }
                else if (boundaryCharsSet.Contains(text[r]) && char.IsLetter(text[l]) && r - l > 1)
                {
                    string word = text.Substring(l, r - l);
                    if (commonWordSet.Contains(word) || commonWordSet.Contains(word.ToLowerInvariant()))
                    {
                        count++;
                    }

                    l = r + 1;
                }
                else if (boundaryCharsSet.Contains(text[r]))
                {
                    l = r + 1;
                }
            }

            return count;
        }