buttonText

The value of the element which represents calendar button. The default value is "select":

<input id="picker" ></input>

<script type="text/javascript">
    $(function () {
        $("#picker").shieldMonthYearPicker({
            messages: {
                calendarIconTooltip: "show calendar",
                buttonText: "button"
            },
        });
    });
</script>