1. by application ( eg mahara does not support enrolments so don't offer it)
2. by service (eg moodle can subscribe to mahara portfolio services but not publish - same for repository)

also it seems very odd that the language strings for a service go in the plugin that published rpc functions to handle them.

eg: for pf_out service, many portfolio plugins would publish rpc functions to that service, but the code looks in the language pack of (some) plugin to find them