Chinese Wikipedia in Chinese, you have the option to read the articles in either the simplified or the traditional characters. What makes it such an excellent experience is that people can edit in the characters they are comfortable with and readers will be presented in what is their preference.
The technology used is well proven and it has been in production for quite some time. It works extremely well within the Wikimedia Foundation but outside the WMF it is not clear or obvious how to implement it.
There have been requests at Wikia for this feature and they would implement it if they know how to. At translatewiki.net we have people localise in both traditional as well as simplified Chinese and with some additional programming it will be possible to cut the needed effort in half.
As Chinese is generating so much traffic for Wikipedia, this is a good moment to make a formal extension out of the current hack. This will make it easy to provide the quality of language support MediaWiki can support everywhere.