We are looking to develop a multilingual group site (each language would have a separate group with sub-groups for countries) and are inquiring about jomsocial's capabilities. Examples of similar live sites would be good as well.
Can you also provide a link to your entry on the JED? We couldn't find it.
Do you mean on each group has own language depend the category countries? I am sorry we dont have this feature, the simplest way you can install translation plugin so you can switch the language manually.