Wait a minute. Let me back up a moment. Are you using GTalk as it’‘s built into the IM Gateway plugin? (if so, you are running a busted version of the plugin that was released without my knowledge, so please re-download the plugin from the openfire plugins page if that’'s the case, you should -not- see XMPP or GTalk in your admin console)
The XMPP server should more or less just be passing the data you send on through to the other side. The data you send is expected to be utf-8 encoded.
The XML parsers are expecting to be “speaking UTF-8” (or at least if they are written well they are), so there shouldn’'t be any problems on that front.