OK, so I still don't understand what problem it is you are reporting.  What do you mean by "can't craete non-valid strings"?  Of course you can't.  (I don't see how you could do that programatically, either, although that depends heavily on your definition of non-valid.)

Are you reporting that cmd.exe has no support for entering French characters?  That wouldn't be a Python bug.

Are you reporting that idle lacks the keyboard support for French?  (I don't use Idle, so I don't know if that is true or not.)