You should use 2.4.3 of pidgin of Ubuntu 8.04 backports:
version 2.4.3 (07/01/2008): libpurple: * Yahoo! Japan now uses UTF-8, matching the behavior of official clients and restoring compatibility with the web messenger (Yusuke Odate)
http://www.pidgin.im/ChangeLog
You should use 2.4.3 of pidgin of Ubuntu 8.04 backports:
version 2.4.3 (07/01/2008):
libpurple:
* Yahoo! Japan now uses UTF-8, matching the behavior of official clients
and restoring compatibility with the web messenger (Yusuke Odate)
http:// www.pidgin. im/ChangeLog