I can't speak for Zotero directly, but I've heard that the core team are busy with completion of the 3.0 client, and that multilingual support is one of the features on the table for 3.5 development. We'll have to wait and see what emerges, but it should be safe to view MLZ/Mulzero as a temporary spur, with a channel for migrating full-multilingual data into the official client/server container when that functionality is ready.