It works for me, I understand how and the code but in case of adding buddypress-activity support to a post type created by another plugin (CBX Poll) I can’t figure out what text domain to use when I put this code in bp-custom.php
With a home made plugin I would add support at post type registration and use this custom plugin’s domain.
I guess I could use the functions.php of the theme and the theme’s domain but then it’s theme dependent.