网上很多坑人的资料，说可以支持小程序的中文，复制来复制去，下面我就把我找来的代码分享出来，亲测有效：
场景：post参数中有中文字符，md5加密出来的和服务器的不一致，所以需要md5支持中文。

代码及使用如下：

var rotateLeft = function (lValue, iShiftBits) {
  return (lValue << iShiftBits) | (lValue >>> (32 - iShiftBits));
}

var addUnsigned = function (lX, lY) {
  var lX4, lY4, lX8, lY8, lResult;
  lX8 = (lX & 0x80000000);
  lY8 = (lY & 0x80000000);
  lX4 = (lX & 0x40000000);
  lY4 = (lY & 0x40000000);
  lResult = (lX & 0x3FFFFFFF) + (lY & 0x3FFFFFFF);
  if (lX4 & lY4) return (lResult ^ 0x80000000 ^ lX8 ^ lY8);
  if (lX4 | lY4) {
    if (lResult & 0x40000000) return (lResult ^ 0xC0000000 ^ lX8 ^ lY8);
    else return (lResult ^ 0x40000000 ^ lX8 ^ lY8);
  } else {
    return (lResult ^ lX8 ^ lY8);
  }
}

var F = function (x, y, z) {
  return (x & y) | ((~x) & z);
}

var G = function (x, y, z) {
  return (x & z) | (y & (~z));
}

var H = function (x, y, z) {
  return (x ^ y ^ z);
}

var I = function (x, y, z) {
  return (y ^ (x | (~z)));
}

var FF = function (a, b, c, d, x, s, ac) {
  a = addUnsigned(a, addUnsigned(addUnsigned(F(b, c, d), x), ac));
  return addUnsigned(rotateLeft(a, s), b);
};

var GG = function (a, b, c, d, x, s, ac) {
  a = addUnsigned(a, addUnsigned(addUnsigned(G(b, c, d), x), ac));
  return addUnsigned(rotateLeft(a, s), b);
};

var HH = function (a, b, c, d, x, s, ac) {
  a = addUnsigned(a, addUnsigned(addUnsigned(H(b, c, d), x), ac));
  return addUnsigned(rotateLeft(a, s), b);
};

var II = function (a, b, c, d, x, s, ac) {
  a = addUnsigned(a, addUnsigned(addUnsigned(I(b, c, d), x), ac));
  return addUnsigned(rotateLeft(a, s), b);
};

var convertToWordArray = function (string) {
  var lWordCount;
  var lMessageLength = string.length;
  var lNumberOfWordsTempOne = lMessageLength + 8;
  var lNumberOfWordsTempTwo = (lNumberOfWordsTempOne - (lNumberOfWordsTempOne % 64)) / 64;
  var lNumberOfWords = (lNumberOfWordsTempTwo + 1) * 16;
  var lWordArray = Array(lNumberOfWords - 1);
  var lBytePosition = 0;
  var lByteCount = 0;
  while (lByteCount < lMessageLength) {
    lWordCount = (lByteCount - (lByteCount % 4)) / 4;
    lBytePosition = (lByteCount % 4) * 8;
    lWordArray[lWordCount] = (lWordArray[lWordCount] | (string.charCodeAt(lByteCount) << lBytePosition));
    lByteCount++;
  }
  lWordCount = (lByteCount - (lByteCount % 4)) / 4;
  lBytePosition = (lByteCount % 4) * 8;
  lWordArray[lWordCount] = lWordArray[lWordCount] | (0x80 << lBytePosition);
  lWordArray[lNumberOfWords - 2] = lMessageLength << 3;
  lWordArray[lNumberOfWords - 1] = lMessageLength >>> 29;
  return lWordArray;
};

var wordToHex = function (lValue) {
  var WordToHexValue = "",
    WordToHexValueTemp = "",
    lByte, lCount;
  for (lCount = 0; lCount <= 3; lCount++) {
    lByte = (lValue >>> (lCount * 8)) & 255;
    WordToHexValueTemp = "0" + lByte.toString(16);
    WordToHexValue = WordToHexValue + WordToHexValueTemp.substr(WordToHexValueTemp.length - 2, 2);
  }
  return WordToHexValue;
};

var uTF8Encode = function (string) {
  string = string.replace(/\x0d\x0a/g, "\x0a");
  var output = "";
  for (var n = 0; n < string.length; n++) {
    var c = string.charCodeAt(n);
    if (c < 128) {
      output += String.fromCharCode(c);
    } else if ((c > 127) && (c < 2048)) {
      output += String.fromCharCode((c >> 6) | 192);
      output += String.fromCharCode((c & 63) | 128);
    } else {
      output += String.fromCharCode((c >> 12) | 224);
      output += String.fromCharCode(((c >> 6) & 63) | 128);
      output += String.fromCharCode((c & 63) | 128);
    }
  }
  return output;
};

function md5(string) {
  var x = Array();
  var k, AA, BB, CC, DD, a, b, c, d;
  var S11 = 7,
    S12 = 12,
    S13 = 17,
    S14 = 22;
  var S21 = 5,
    S22 = 9,
    S23 = 14,
    S24 = 20;
  var S31 = 4,
    S32 = 11,
    S33 = 16,
    S34 = 23;
  var S41 = 6,
    S42 = 10,
    S43 = 15,
    S44 = 21;
  string = uTF8Encode(string);
  x = convertToWordArray(string);
  a = 0x67452301;
  b = 0xEFCDAB89;
  c = 0x98BADCFE;
  d = 0x10325476;
  for (k = 0; k < x.length; k += 16) {
    AA = a;
    BB = b;
    CC = c;
    DD = d;
    a = FF(a, b, c, d, x[k + 0], S11, 0xD76AA478);
    d = FF(d, a, b, c, x[k + 1], S12, 0xE8C7B756);
    c = FF(c, d, a, b, x[k + 2], S13, 0x242070DB);
    b = FF(b, c, d, a, x[k + 3], S14, 0xC1BDCEEE);
    a = FF(a, b, c, d, x[k + 4], S11, 0xF57C0FAF);
    d = FF(d, a, b, c, x[k + 5], S12, 0x4787C62A);
    c = FF(c, d, a, b, x[k + 6], S13, 0xA8304613);
    b = FF(b, c, d, a, x[k + 7], S14, 0xFD469501);
    a = FF(a, b, c, d, x[k + 8], S11, 0x698098D8);
    d = FF(d, a, b, c, x[k + 9], S12, 0x8B44F7AF);
    c = FF(c, d, a, b, x[k + 10], S13, 0xFFFF5BB1);
    b = FF(b, c, d, a, x[k + 11], S14, 0x895CD7BE);
    a = FF(a, b, c, d, x[k + 12], S11, 0x6B901122);
    d = FF(d, a, b, c, x[k + 13], S12, 0xFD987193);
    c = FF(c, d, a, b, x[k + 14], S13, 0xA679438E);
    b = FF(b, c, d, a, x[k + 15], S14, 0x49B40821);
    a = GG(a, b, c, d, x[k + 1], S21, 0xF61E2562);
    d = GG(d, a, b, c, x[k + 6], S22, 0xC040B340);
    c = GG(c, d, a, b, x[k + 11], S23, 0x265E5A51);
    b = GG(b, c, d, a, x[k + 0], S24, 0xE9B6C7AA);
    a = GG(a, b, c, d, x[k + 5], S21, 0xD62F105D);
    d = GG(d, a, b, c, x[k + 10], S22, 0x2441453);
    c = GG(c, d, a, b, x[k + 15], S23, 0xD8A1E681);
    b = GG(b, c, d, a, x[k + 4], S24, 0xE7D3FBC8);
    a = GG(a, b, c, d, x[k + 9], S21, 0x21E1CDE6);
    d = GG(d, a, b, c, x[k + 14], S22, 0xC33707D6);
    c = GG(c, d, a, b, x[k + 3], S23, 0xF4D50D87);
    b = GG(b, c, d, a, x[k + 8], S24, 0x455A14ED);
    a = GG(a, b, c, d, x[k + 13], S21, 0xA9E3E905);
    d = GG(d, a, b, c, x[k + 2], S22, 0xFCEFA3F8);
    c = GG(c, d, a, b, x[k + 7], S23, 0x676F02D9);
    b = GG(b, c, d, a, x[k + 12], S24, 0x8D2A4C8A);
    a = HH(a, b, c, d, x[k + 5], S31, 0xFFFA3942);
    d = HH(d, a, b, c, x[k + 8], S32, 0x8771F681);
    c = HH(c, d, a, b, x[k + 11], S33, 0x6D9D6122);
    b = HH(b, c, d, a, x[k + 14], S34, 0xFDE5380C);
    a = HH(a, b, c, d, x[k + 1], S31, 0xA4BEEA44);
    d = HH(d, a, b, c, x[k + 4], S32, 0x4BDECFA9);
    c = HH(c, d, a, b, x[k + 7], S33, 0xF6BB4B60);
    b = HH(b, c, d, a, x[k + 10], S34, 0xBEBFBC70);
    a = HH(a, b, c, d, x[k + 13], S31, 0x289B7EC6);
    d = HH(d, a, b, c, x[k + 0], S32, 0xEAA127FA);
    c = HH(c, d, a, b, x[k + 3], S33, 0xD4EF3085);
    b = HH(b, c, d, a, x[k + 6], S34, 0x4881D05);
    a = HH(a, b, c, d, x[k + 9], S31, 0xD9D4D039);
    d = HH(d, a, b, c, x[k + 12], S32, 0xE6DB99E5);
    c = HH(c, d, a, b, x[k + 15], S33, 0x1FA27CF8);
    b = HH(b, c, d, a, x[k + 2], S34, 0xC4AC5665);
    a = II(a, b, c, d, x[k + 0], S41, 0xF4292244);
    d = II(d, a, b, c, x[k + 7], S42, 0x432AFF97);
    c = II(c, d, a, b, x[k + 14], S43, 0xAB9423A7);
    b = II(b, c, d, a, x[k + 5], S44, 0xFC93A039);
    a = II(a, b, c, d, x[k + 12], S41, 0x655B59C3);
    d = II(d, a, b, c, x[k + 3], S42, 0x8F0CCC92);
    c = II(c, d, a, b, x[k + 10], S43, 0xFFEFF47D);
    b = II(b, c, d, a, x[k + 1], S44, 0x85845DD1);
    a = II(a, b, c, d, x[k + 8], S41, 0x6FA87E4F);
    d = II(d, a, b, c, x[k + 15], S42, 0xFE2CE6E0);
    c = II(c, d, a, b, x[k + 6], S43, 0xA3014314);
    b = II(b, c, d, a, x[k + 13], S44, 0x4E0811A1);
    a = II(a, b, c, d, x[k + 4], S41, 0xF7537E82);
    d = II(d, a, b, c, x[k + 11], S42, 0xBD3AF235);
    c = II(c, d, a, b, x[k + 2], S43, 0x2AD7D2BB);
    b = II(b, c, d, a, x[k + 9], S44, 0xEB86D391);
    a = addUnsigned(a, AA);
    b = addUnsigned(b, BB);
    c = addUnsigned(c, CC);
    d = addUnsigned(d, DD);
  }
  var tempValue = wordToHex(a) + wordToHex(b) + wordToHex(c) + wordToHex(d);
  return tempValue.toLowerCase();
}
module.exports.md5 = md5

小程序中md5使用方法：

var utilMd5 = require('/md5.js');  
var sign = utilMd5.md5(kvStr);