As per #6368, "Join Group Chat" for a normal gtalk account fails silently. The behavior is exactly the same in the latest 1.2.1 as that ticket specifies, as is the unhelpful debug log output. Although, for one of my failed attempts to test@talk.google.com I did get a dialog exactly 26 minutes later that it had failed: 404: Remote Server Not Found
The reasons these fail are that the default server is incorrect (conference.talk.google.com but should be groupchat.google.com) and gtalk requires a special Chat Room Name convention (private-chat-12345678-dead-beef-feed-fedcba987654 as per http://mkokotovich.blogspot.com/2007/12/google-talk-groupchat.html). Also the password is not needed, as Google just checks that you're logged in to your account.
Changing these defaults to the correct server and a randomly generated chat room name of that format would enable average google talk users to join group chats via Adium.
