BuddyPress.org

Yep, it’s a good idea to relocate it, but the path was still wrong. The constant BP_PLUGIN_DIR points to the BP folder. Then you have the wp-content folder, so right there’s the problem. You could use this:
load_textdomain( ‘buddypress’, WP_PLUGIN_DIR . ‘/bp-languages/bp-family-’ . BPLANG . ‘.mo’ );

This assumes that you have your folder structure like this:
wp-content/plugins/bp-languages