检测字符串的中英文

using System.Text.RegularExpressions;

Regex regChina = new Regex("^[^\x00-\xFF]");
            Regex regEnglish = new Regex("^[a-zA-Z]");
            string str = "啊aaa";
            if (regEnglish.IsMatch(str))
            {
                MessageBox.Show("是英文");
            }
            else if (regChina.IsMatch(str))
            {
                MessageBox.Show("是中文");
            }