I'm too exited to keep this to myself. It has to be tested further, with other browsers and on other platforms, and with people that can write Chinese, but since this could be useful to other double byte languages, here a way to create a story in Simplified Chinese (GB2312) in a Manila site. Thanks to Keola Donaghy who gave me judicious advices.
Here's what I did. The server run Frontier 7.0.1 on Mac OS 9.0.4.
(A) Paste
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
in Prefs->Advanced->Template in the header of the template.
(B) Set MyManilaWebsite.["#prefs"].isoFilter to false. If it doesn't exists, create it.
(C) On the Mac, at MyManilaWebsite.["#filters"].finalFilter, add this line to the filter:
pta^.renderedText = string.macToLatin (pta^.renderedText)
(1)

I have copied the chinese text from the source of this page.

Here's the text is pasted in OS X Internet Explorer 5.1. The server is on Mac OS 9.0.4.
(I tried the same thing in Windows 98/IE 5 with success)

The result. Life is good! Chinese ideograms are wonderful!
Please note that since isoFilter is false, the accented characters are not converted to HTML entities.
(my family name is Décarie, not Dcarie)