tr [:upper:] [:lower:] with Cyrillic text

Question

I'm trying to extract a word list from a Russian short story.

#!/bin/sh

export LC_ALL=ru_RU.utf8

sed -re 's/\s+/\n/g' | \
sed 's/[\.!,—()«»;:?]//g' | \
tr '[:upper:]' '[:lower:]' | \
sort | uniq

However the tr step is not lowercasing the Cyrillic capital letters. I thought I was being clever using the portable character classes!

$ LC_ALL=ru_RU.utf8 echo "Г" | tr [:upper:] [:lower:]
Г

In case it's relevant, I obtained the Russian text by copy-pasting from a Chrome browser window into Vim. It looks right on screen (a Putty terminal). This is in Cygwin's bash shell -- it should work identically to Bash on Linux (should!).

What is a portable, reliable way to lowercase unicode text in a pipe?

Answer 1

This is what I found at Wikipedia (without any reference, though):

Most versions of tr, including GNU tr and classic Unix tr, operate on single-byte characters and are not Unicode compliant. An exception is the Heirloom Toolchest implementation, which provides basic Unicode support.

Also, this is old but related.

As I mentioned in the comment, sed seems to work (GNU sed, at least):

$ echo 'СТЭК' | sed 's/[[:upper:]]*/\L&/'
стэк