Hi Martin, indeed, here in my workplace Windows machine there is no "CP_UTF_8" codepage, nor there is 65001. I was waiting to try it later on my home machine, but since you say it's broken, then I'll need to look for a way to convert the actual string to the 850 codepage...
Just for info, this is probably a d related bug, because the Racket language for example has a (reencode-output-port) function, and it Works. Greetings, Cleverson