I have a RAR file with non ASCII letters in filenames. I tried decoding it in Delphi. My code works fine for ASCII filenames but it failed on these. It is not WideChar, nor UTF8. I found RAR specs here: http://ams.cern.ch/AMS/amsexch/arch/rar/technote.txt but it says nothing about the character encoding. I tried WOTSIT.org but all links to RARs are dead (almost every link is dead there; I even contacted admin but he didn't respond and didn't fix links). It seems it is not an 8bit encoding, but no idea what could it be.
This is the only paragraph that says something about the name:
0x200 - FILE_NAME contains both usual and encoded
Unicode name separated by zero. In this case
NAME_SIZE field is equal to the length
of usual name plus encoded Unicode name plus 1.
If this flag is present, but FILE_NAME does not
contain zero bytes, it means that file name
is encoded using UTF-8.
It seems that it is UTF-8, but you say it is not. Can you try again?