Every copy of Mac OS X 10.3 (Panther), 10.4 (Tiger), 10.5 (Leopard), 10.6 (Snow Leopard), and 10.7 (Lion) comes with built-in multilingual support that includes Chinese. In addition, all OS 9 CDs worldwide include Chinese support.
"WorldScript" is Apple's trademark for the technology that supported multiple languages on Macintosh computers before OS X. It remains as part of the Carbon framework in OS X. In WorldScript, each language has a "script" that supports character-set and encoding standards for that language. Scripts also contain instructions for handling text, sorting characters, and so on. WorldScript provides two distinct Chinese scripts: Traditional Chinese, based on Big Five, and Simplified Chinese, based on GB 2312. A "WorldScript-savvy" application is able to correctly input, display, store, and print text in the standard encodings supported by WorldScript and the Mac OS.
The Unicode standard is a multilingual encoding that has absorbed the character sets of both Big Five and GB 2312, as well as those of various other Chinese, Japanese, and Korean (CJK) encodings. As of version 6.0 (October 2010), Unicode contains 74,616 distinct CJK Unified Ideographs. A "Unicode-savvy" application has the ability to correctly input, display, store, and print Unicode characters in all planes. Chinese is a relatively simple script (as opposed to complex Indic and Arabic scripts, for example), so basic Unicode support is usually enough. The only real problem is that some applications still don't support code points beyond Unicode's Basic Multilingual Plane. [See Ken Lunde on this problem.]
With regard to Chinese text, the vast majority of applications available today are Unicode-savvy. Unless you are running legacy applications in the Classic environment or an older version of OS X, it is no longer very likely that you'll need to know much of anything about WorldScript. There was a time when it was crucial to know something about character sets, encodings, document formats, and the like, especially for Mac OS users working in Chinese at the height of Windows' dominance. That frustration and confusion was the main impetus for the establishment of this web site back then, not so long ago. Thanks to Unicode, that era has passed.
One notable exception to this trend is Chinese fonts. Unicode places a special burden on typography when it comes to CJK characters, glyphs, and variants. For most users, it is enough to know whether a Chinese font covers Traditional Chinese (Big Five), Simplified Chinese (GB 2312), or both (Unicode, GBK, GB 18030). More advanced users will, however, need an understanding of these and other character sets, along with the typography of glyph variants, in order to handle Chinese fonts in a professional manner.
The essential text is the second edition of CJKV Information Processing by Ken Lunde (O'Reilly, 2008). Lunde has a Ph.D. in linguistics and is manager of CJKV type development at Adobe. The comprehensive understanding it provides is unmatched. Nothing else comes close, online or otherwise. See: http://oreilly.com/catalog/9780596514471/
Multilingual Mac provides current information and troubleshooting help: http://m10lmac.blogspot.com/
Ideographer publishes excellent articles (in Chinese) on interesting and sometimes undocumented aspects of using CJK languages on OS X: http://www.ideographer.com/articles/
CJK Type is a blog based at Adobe's Beijing office: http://blogs.adobe.com/CCJKType/
Pinyin Joe maintains the Chinese Computing Help Desk, a well-organized and informative guide to using Chinese on Windows XP and above: http://www.pinyinjoe.com/
This web site was founded (elsewhere) in 1998 by Eric Rasmussen, with help and advice from Kerim Friedman.
Many people have helped out as the site has developed over the years, including Aki Abe, Iwo Amelung, Steven Angle, Charles Belov, Michael Brasser, Kai-shao Chen, Nien-po Chen, Cynthia Col, Jason Cox, Christopher Cullen, Douglas Davidson, John Delacour, Dale Dellinger, Rard Denissen, Tom Gewecke, Rickford Grant, Fritz Grohmann, Bob Hall, Zev Handel, Jeffrey Hayden, Matthew Hills, Timothy Huang, Nobumi Iyanaga, Nina Jalladeau, Fuxue Jin, Charles Lee, Eugene Lee, Henry Leperlier, Magnus Lewan, Joe Lewis, Lukhnos D. Liu, Nello Lucchesi, Xinjiang Lü, Andrew Main, Patrick Moran, Tee Peng, Jens Østergaard Petersen, Greg Pringle, Sven Rossbach, Jacques Rougeaux, Leo Shin, Jonathan Skaff, Robert Smitheram, Leo So, Edward Spodick, Glenn Tiffert, Kelvin Tsang, Ken Tsang, Hsu-min Tseng, Shiangtai Tuan, Etienne de la Vaissière, Sue Wiles, Joe Wicentowski, Amnon Yaish, Weizhong Yang, Dominic Yu, Weiyun Yu, Eddie Yuen, Peide Zha, and Allen Zhao.