Modern Medley Interlisp can read and write files where 16 bit character codes are represented as UTF-8 byte sequences or UTF-16 byte-pairs, and convert from and to Unicode codes to equivalent internal Medley codes. For details see:
https://files.interlisp.org/medley/library/UNICODE.TEDIT.pdf
The open source project to preserve, revive, and modernize Medley Interlisp. This extensible graphical operating and programming environment has roots in Xerox's Palo Alto Research Center (PARC).