JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/jqueryui/1.12.1/themes/smoothness/jquery-ui.min.css">
<script src="https://code.jquery.com/jquery-3.2.1.min.js"></script>
<script src="https://code.jquery.com/ui/1.12.1/jquery-ui.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jqueryui/1.11.1/i18n/jquery-ui-i18n.min.js"></script>
<h3>Japanese JQuery UI Datepicker</h3>
<input type="text" id="japaneseCalendar"/>

CSS

#ui-datepicker-div {
        font-size: 14px;
    }

JavaScript

$(document).ready(function () {
        var userLang = navigator.language || navigator.userLanguage;

        var options = $.extend({},
            $.datepicker.regional["pt"], {
                dateFormat: "yy/mm/dd",
                changeMonth: true,
                changeYear: true,
                highlightWeek: true
            }
        );

        $("#japaneseCalendar").datepicker(options);
    });