I am by no means a BuddyPress expert, but on our sites we’ve changed the text you see when you click on “Change Profile Photo” by overriding the file change-avatar.php. In other words, I’ve made a copy of that file, changed the text to say what I want, and then put that file in wp-content/themes/MY_CHILD_DIR/buddypress/members/single/profile. We’re not using Nouveau, so that might make a difference.

If you’ve actually changed the text directly in the original buddypress file it seems weird (to me) that the change didn’t take (unless it’s already being overridden).

I doubt that helps. Maybe you’ll get a better answer from somebody who knows more.