Here's a small tip to get UTF-8 to work properly in irssi running within GNU screen:
Add the following to ~/.screenrc
Then start screen with the -U parameter, and start irssi.
/set term_charset utf-8 /set recode_autodetect_utf8 ON /save
Also add the following to your ~/.bashrc, but it may not be required:
export LANG=en_US.UTF-8 export LC_CTYPE=en_US.UTF-8
UTF-8 encoding now works, it's as simple as that. (Note for reference, I've only tested this within Terminal.app on OS X). Next time you re-attach to this screen, remember to do so with the -UrD parameter.
TedSki on #motorcycles (EFNet IRC) came up with this solution and told me about it. Here's after the first test:
[20:37] < sgtzx> let's give it another shot [20:37] < TedSki> sgtzx: 華語 [20:37] < sgtzx> yes, works! [20:37] < TedSki> there ya go