饼干中的乱码字符

我在cookie中存储了汉字,但cookie值变为乱码。我该怎么办?

function createCookie(name, value, days) {
    if (days) {
        var date = new Date();
        date.setTime(date.getTime() + (days * 1000 * 60 * 60 * 24));
        var expires = "; expires=" + date.toGMTString();
    }
    else var expires = "";
    document.cookie = name + "=" + value + expires + "; path=/";
}

createCookie("city", decodeURI('%e6%b8%a9%e5%b7%9e%e5%b8%82'));
alert(decodeURI('%e6%b8%a9%e5%b7%9e%e5%b8%82')); // The Chinese characters are correct
alert(document.cookie); //The Chinese characters are corrupted