From an email from jw:

- autodetect mode. In this mode screen does not believe anything ioctl()'s
  or environment tell it about the terminal.
  It probes to see how the cursor moves when sending several test codes.
  E.g. if UTF8 a-umlaut  moves two positions, then we are probably running
  in latin1 land. If a latin1 a-umlaut does not move the cursor at all,
  then dumb font is loaded.
  It also monitors what comes in from the application for typical latin1
  codes, and for illegal UTF8 codes.
  This should bring screen on the right track pretty soon.
  After all probing is done, screen should also be able to print a
  sugestion how the environment should be fixed, so that the applications
  work correctly.
  I'd implement the prototype of this autodetect logic as a perl script,
  to learn what is doable, and experiment with heuristics.