I've consulted with Wan-Teh Chang, the NSPR module owner, regarding Unicode support. Apparently, Unicode support has been added to NSPR's file I/O functions (to support Unicode file pathnames). However, the new functions have only been implemented on Windows. Moreover, they are conditionally compiled only if the MOZ_UNICODE macro is defined.
Searching for that macro leads to functions for opening files and directories. I'm not sure that's what I'm looking for or if it's useful to what I'm doing. I'm a bit confused, because I know already that nsIFile (or nsILocalFile) supports Unicode for paths and filenames. And I have no idea what to do about Unix and Unicode. That's actually a much bigger problem in nsIProcess because Mac and Linux both call PR_CreateProcess, whereas I have the option of avoiding that with Windows with existing code.
Wan-Teh indicated that a Unicode variant of PR_CreateProcess is something that could make it into the tree.
