<select id="lang" class=" form-control">
	<option value="zh">中文</option>
	<option value="en">English</option>
</select>

$(function () {
	//是否存在语言项
   if (!localStorage.currentLang) {
        //本地存储当前选中语言
        localStorage.currentLang = $('#lang option:selected').val();
    } else {
        //定义当前语言
        var currLang = localStorage.currentLang;
        $("#lang option[value=" + currLang + "]").attr("selected", true);
        $("#lang").on('change', function () {
           //存储当前选中的语言
        localStorage.currentLang = $(this).children('option:selected').val();
        //刷新  单页面可以注释
        location.reload();
    });
}
langString(localStorage.currentLang)

<label data-i18n="username">用户名</label><input type="text">

$.i18n.prop('key')