I just came across something similar to this post as well through applying the same system-wide utf-8 setting. Decided to apply the setting in Windows (10, 22H2) to avoid having to deal with (many, many) encoding issues with various dev & code tools, command prompt, batch files, python/powershell scripts and so on.
For example, the box line drawing chars are mostly OK, but the parts which are filled placeholders seem to be awry:

And the whole box around the Statistics (/) is completely off:

Running ZTree from a CMD prompt which has been switched back to CP 437, 850 or 1252 makes no difference, these errant lines are still just represented with the Unicode replacement character.
For the most part, ZTree works OK with Unicode chars in filenames and directories, and the Directory view works just fine, so in some parts, these chars are certainly handled correctly but there's a few niggles here and there which just seem like incorrectly encoded static strings or consts, or perhaps the declare file or source file which includes these strings is incorrectly encoded...