SMF2.1/Themes/default/languages/Alerts.english.php

<?php
// Version: 2.1 Alpha 1; Alerts

$txt['topic_na'] = '(private topic)';
$txt['board_na'] = '(private board)';

$txt['unread_alerts'] = 'Unread';
$txt['all_alerts'] = 'All alerts';
$txt['mark_alerts_read'] = 'Mark read';
$txt['alert_settings'] = 'Settings';
$txt['alerts_no_unread'] = 'No unread alerts.';

$txt['alert_msg_like'] = '{member_link} liked your post {msg_msg}';
$txt['alert_member_register_standard'] = '{member_link} just signed up';
$txt['alert_member_register_approval'] = '{member_link} just signed up (account requires approval)';
$txt['alert_member_register_activation'] = '{member_link} just signed up (account requires activation)';
$txt['alert_member_group_request'] = '{member_link} has requested to join {group_name}';
?>