Zip archives don't store information about the encoding of the file names inside, so BetterZip has to guess what the encoding might be. It always works with UTF-8 files (like those created on a Mac), but can't always figure out the encoding of Windows created archives. The result when you extract the archive with Mac OS X' built in Archive Utility is probably the same, right? I will add the ability to choose the right encoding manually in a future version.