If someone were to port Ruby to Windows/CE, they would have a little 
problem: Ruby seems to assume (from a quick glance at the source) that 
filenames are made up of 1-byte characters (don't know what character set 
it assumes). However, all file APIs in Windows/CE take and return Unicode 
characters.

Other WinCE ports (like the Python WinCE port) just attempt to map the 
characters back and forth to ASCII (or maybe just some unspecified 8-bit 
character set). However, this can lose a lot of information if you have 
users who have used the native ability to use their local character set for 
filenames.

Are there any provisions in the Ruby source for dealing with wide-character 
filenames?

I would think that (given its wide use in Japan) this would be an important 
feature.

Note that Windows/NT also provides a set of Unicode APIs equivalent to the 
ASCII ones for file operations.