It took me some time to reproduce the problem. Here is the minimal HTML:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<!-- jQuery 2.0.2 -->
<script type="application/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/2.0.2/jquery.min.js"></script>
<script type="application/javascript" src="tableExport.js"></script>
<script type="application/javascript" src="jquery.base64.js"></script>
<script type="application/javascript" src="jspdf/libs/sprintf.js"></script>
<script type="application/javascript" src="jspdf/jspdf.js"></script>
<script type="application/javascript" src="jspdf/libs/base64.js"></script>
</head>
<body>
<table id="nation">
<tbody>
<tr>
<td>
中国
</td>
</tr>
</tbody>
</table>
<a href="#" onclick ="$('#nation').tableExport({type:'pdf',escape:'false'});">PDF</a>
</body>
</html>
Here is the complete folder (including the js) so you can test locally: http://bit.ly/1fW0YbX.
If you look at the generated PDF, it only uses the standard PDF font Helvetica which supports the Latin-1 character set only. This is why you do not see the expected Japanese glyphs. I couldn't find any related option for the HTML table export jquery plugin so I guess it just isn't supported. But maybe I am missing a localization plugin.