To answer the original question: here is how you decode utf-8 in javascript:
http://ecmanaut.blogspot.ca/2006/07/encoding-decoding-utf8-in-javascript.html
Specifically,
function encode_utf8(s) {
return unescape(encodeURIComponent(s));
}
function decode_utf8(s) {
return decodeURIComponent(escape(s));
}
We have been using this in our production code for 6 years, and it has worked flawlessly.
Note, however, that escape() and unescape() are deprecated. See this.