There is not solution because there is no such problem, as soon as your font supports Unicode. Make sure you do not convert text into ANSI or any other non-Unicode encoding before encryption. It's the best to treat the text as UTF-8, see http://msdn.microsoft.com/en-us/library/system.text.utf8encoding.aspx
]. The encoding converts text from/to array of bytes which should be further encrypted/decrypted.
If you still cannot overcome this confusion, you may want to make a short code sample (really short, some 5 lines or so) to show what are you doing. I would be able to find out what's wrong. Use "Improve question".
But first, please try to sort it out yourself.