I can see that Unicode file names can be stored in the ExtraHeaders property of a ZippedFile, and this appears to be working since I can see this value being stored when I examine the zip file with a hex editor. I can see both the ASCII file name and the double-byte Unicode file name for each zip entry.
However, when extracting the zip archive, I’m not sure how to retrieve that Unicode file name from the ExtraHeaders property. Just using the zippedFile.Name returns the ASCII representation of the file name (which will contain ??? where non-english characters exist).