I am afraid node.js doesn't ship with full internationalization support by default.
I would recommend to use a third-party library that will do the job for you.
Or if you use chrome-pdf, one option is also to do the localization task through page javascript. However the previous option is probably better.
<div id='a'>a</div> <script> document.getElementById('a').innerHTML = new Date().toLocaleString('ko-KR') </script>