So a disk (actually a volume) driver should be able to make a .iso?
I believe that support for non-ANSI characters in mkisofs exist, it may depend on the EXACT version you are using and possibly even the build.
You can try this build of xorriso for windows:
but I have no idea if it supports "extended" characters.
But are you sure-sure you are using the "right" commands?
I mean, Unicode characters are only Joliet or Rock Ridge AFAICR and anyway there are limitations in length.
You still could make a filesystem image (i.e. with iMDISK) add to the image the files you want, then save the file and "burn" the file to the .iso, or you could use hard disk emulation:
An alternative could be using UDF (as opposed to ISO9960), *like* :
if for any reason your mkisofs doesn't work with the above both imgburn and cdburnerxp command line should support UDF.