Translate Text using gettext filter/hook

<?php

/**
 * Translate Text using gettext filter/hook
 * As for where to paste this : http://wp-events-plugin.com/tutorials/how-to-safely-add-php-code-to-wordpress/
 */
function change_label( $translated_text, $text, $domain ) {
        switch ( $translated_text ) {
            case 'Add another booking' :
                $translated_text = 'Add another booking. Test';
                break;
            case 'Booking Successful' :
                $translated_text = 'Booking Successful. Test';
                break;
            case 'Clear Selected' :
                $translated_text = 'Clear Selected. Test';
                break;
            case 'Cancel Reservation :
                $translated_text = 'Cancel Reservation. Test';
                break;
            case 'Booking Invoice':
                $translated_text = 'Booking Invoice. Test';
                break;
            case 'Confirm Booking?':
                $translated_text = 'Confirm Booking?. Test';
                break;

        }
    return $translated_text;
}
add_filter( 'gettext', 'change_label', 100, 3 );