The best way to approach a multilingual buddypress install is to set up a WordPress Multisite and use/link each new site as a language alternative to the primary/parent site. Obviously, you would have to network activate BuddyPress plugin too!
Cavaet: This is highly laborious if you are managing things single-handedly. But in the long run, you won’t have any such worries as abrupt stop to the development of an important plugin e.g. buddypress-multilingual, etc.
More so, you will be required to translate virtually ALL your plugins’ settings for each language equivalent of your primary site, install the necessary wordpress language .po and .mo files in your wp-content directory (the less popular Zanto plugin already does a great job and you can use different language in the backend and on the frontend section simultaneously).
Use Network Shared Media plugin to share media across ALL sites in your network (with attendant challenges of its own).
This route is for brave hearts (very experienced webmasters/PHP developers) out there.
The obvious lazy and quick way of doing this is by utilising such plugins as BuddyPress Multilingual, et al.
