ed predates the existence of unicode and has made no changes to support it. So it does not "support" unicode but works fine with UTF-8 if your terminal supports

ed predates the existence of unicode and has made no changes to support it. So it does not "support" unicode but works fine with UTF-8 if your terminal supports it. As far as ed is concerned some bytes are being pushed around between stdin/stdout/your file, and it does not mangle them so everything works.