These currently serialize as external links:
echo '<link rel="mw:WikiLink/Language" href="http://ko.wikipedia.org/wiki/">' | node parse --html2wt [[http://ko.wikipedia.org/wiki/]] echo '<a rel="mw:WikiLink/Interwiki" href="http://ko.wikipedia.org/wiki/">ko:</a>' | node parse --html2wt [[http://ko.wikipedia.org/wiki/|ko:]]
We should probably match absolute URLs against the list of patterns and serialize to the locally defined interwiki / language prefix when that is defined.