You'll need to be more specific with what you're trying to do.

Are you trying to encode the character so that it can be transported in ASCII, and then recovered? If so, you might take a look at techniques that HTTP (URI encoding) and HTML (Entity encoding) use, or the many versions of mail encodings (quoted printable, etc.)

Are you trying to approximate the character? Ie, 'é' -> 'e'. (this one's a bit tricker...I'm guessing someone has a map out there to give you a starting point, I just don't know where...but there's probably a module in CPAN to do it). Of course, this only really works well for some languages (what to you do with Chinese characters?)