Thanks for pointing that out. I stand corrected. (To their credit, this is one case where the ruby docs are clear: "... Note: case replacement is effective only in ASCII region.") Oh well, room for improvement there.

Update: FWIW, a ruby user can do "gem install unicode_utils", and then do things like:

#!/usr/bin/env ruby

require 'unicode_utils'

puts UnicodeUtils.downcase("Я")  # aka "\u042F", "CYRILLIC CAPIT
+AL LETTER YA"
[download]

It's clunky, but it works. (I wish the "code" tags here would allow a letter like "Я" to appear as such.)