>Returns question mark.
>Result should be Ü character, single byte 0xDC. Those 4 bytes per character are returned in WinHttpRequest.ResponseText. How to get 0xDC result ?

Possibly the result you are getting is double width text, so you may need to do strconv() twice - first utf8 to double width, then that to 1257, I think the parameter is 2. I think I had cases when I had to do that (in my case, to 1250).