I installed cr3-qt-win32-3.0.56-10.zip on Windows7 and loaded a utf8 text file. The Chinese characters all display as "?" chars in the main window. However the table of content displays correctly Chinese characters. Selecting text from cr3 and pasting in another application will display the Chinese characters in the other application. So the problem seems to be a display problem rather than an encoding one. I tried other available fonts to no avail.
The text file I used is displayed correctly by CR3/Linux and CR3/Android. The Window7 machine handles Chinese without problems in other apps.