Hello. I can see SINGULAR and PLURAL for action:
APP_GROUP_PHOTOS_NOTIFICATIONS_COMMENTED_ON_YOUR_PHOTO_ALBUM_PLURAL="%1$s posted a comment on your album, {b}%2$s{/b}"
APP_GROUP_PHOTOS_NOTIFICATIONS_COMMENTED_ON_YOUR_PHOTO_ALBUM_SINGULAR="%1$s posted a comment on your album, {b}%2$s{/b}"
so translated it
APP_GROUP_PHOTOS_NOTIFICATIONS_COMMENTED_ON_YOUR_PHOTO_ALBUM_PLURAL="%1$s оставили комментарии к вашему альбому {b}%2$s{/b}"
APP_GROUP_PHOTOS_NOTIFICATIONS_COMMENTED_ON_YOUR_PHOTO_ALBUM_SINGULAR="%1$s оставил(а) комментарий к вашему альбому {b}%2$s{/b}"
But in fact when few users comment my album I always see SINGULAR version.
Thanks.