There has been a lot of excellent work done on Unicode in Squeak.
Unfortunately, not all of it works 'out of the box'.

I've started working on trying to figure out how to enable the basic
operations (input, display, and copy/paste) for several languages.
With the kind help of several Russian squeakers, I've managed to
create relatively simple instructions on how to do so for Russian,
which I've posted here: http://wiki.squeak.org/squeak/5773 ; I've
personally tested the 3.10 instructions under Linux.  However, getting
to this point involved days of experimentation, including quite a lot
of image hangs.  The reason I created the documentation was that,
despite reading everything on squeak.org and the mailing list archives
about Russian and Cyrillic support, I still couldn't get it working -
it took combining the instructions of two people who had had similar
experiences, and the patches of two others, to have everything work,
although there are some problems with garbage characters with
copy/paste sometimes.

A side effect of these instructions is that various accented European
characters (such as à, å, ò, ö, ĵ, ñ, ç, č, ć, š, đ, etc - everything
I've tried) work.  This cursory testing suggests that
Italian/French/German/Spanish/Swedish/Esperanto/Slovenian/etc
operations also work after following the Russian instructions; they do
not work by default.  Perhaps more interestingly, Thai and Greek also
work; Arabic nearly does, but only displays in its 'general Unicode'
form (rather than correctly changing what appears based on the
position of each letter in the word: see
http://en.wikipedia.org/wiki/Arabic_alphabet for a better
description).

I'm now going through the same process for Japanese.  Installing
'Japanese Environment Installer' (JEI) from SqueakMap only gave me a
working display of Japanese characters, without working input or
copy/paste.  Possibly interestingly, direct input while using a
Japanese keymap (with no input method) to type kana works with the
Russian patches, but not with the JEI patches.

Nothing using extra input method software works anywhere in Squeak in
any configuration I've tried.  Deadkeys also don't work.

I would like to request help from all Squeakers who can input,
display, and copy/paste text in languages which have characters or
writing systems that don't appear in the languages mentioned above,
and especially of those who have everything working with Japanese.
Any instructions on how you did it would be greatly appreciated.  I
intend to keep documenting the simplest ways to currently set things
up, which will hopefully have the side effect of making a baseline set
of patches to have things Just Work become clear.  Any reports of
errata in the documentation, platform differences, or bugs are also
extremely welcome.

Thank you;
Katerina Barone-Adesi