[Alberto]

It seems like the “bp_nav” is deprecated, now I use te code below to change the tab labels:

function ns_profile_tab_labels() {

  global $bp;

  $bp->members->nav->edit_nav( array(
    'name' => __('My Timeline', TEXT_DOMAIN),
  ), 'activity' );

  $bp->members->nav->edit_nav( array(
    'name' => __('My Connections', TEXT_DOMAIN),
  ), 'friends' );

  $bp->members->nav->edit_nav( array(
    'name' => __('My Profile', TEXT_DOMAIN),
  ), 'profile' );

  $bp->members->nav->edit_nav( array(
    'name' => __('My Groups', TEXT_DOMAIN),
  ), 'groups' );

  $bp->members->nav->edit_nav( array(
    'name' => __('My Photos', TEXT_DOMAIN),
  ), 'photos' );

}

add_action( 'bp_setup_nav', 'ns_profile_tab_labels', 1000 );

Goes in your functions.php