How to convert Å letter to AA?

Hello, I’m lookking help how to convert Å letter into AA. I’m able convert Ö to O, Å to A and Ä to A, but I need to get double AA from Å. So far best worked System.Text.Encoding.UTF8.GetString(System.Text.Encoding.GetEncoding(“ISO-8859-8”).GetBytes(str_string))