Andrew, please reopen this issue. Your committed patch does not work if IDLE is not using the subprocess.

    >>> got_ahsa = "\N{GOTHIC LETTER AHSA}"
    >>> got_ahsa
    Traceback (most recent call last):
      File "<pyshell#1>", line 1, in <module>
        got_ahsa
      File "idlelib/PyShell.py", line 1255, in write
        return self.shell.write(s, self.tags)
      File "idlelib/PyShell.py", line 1233, in write
        'Non-BMP character not supported in Tk')
UnicodeEncodeError: 'UCS-2' codec can't encode characters in position 1-1: Non-BMP character not supported in Tk

However, it does work when IDLE uses a subprocess.