I guess you have read this? ->
forum.joomla.org/index.php?topic=55065.0
Also check your joomla/language/yourlanguage.php
> Open the file, change the charset, so the line readsDEFINE('_ISO','charset=utf-8');
This file should be then saved as utf-8 without BOM
Your SMF is also UTF-8, and the database too?
Under SMF 1.1. Final there is a new choice - Admin>Forum maintenance>Convert to UTF-8