Forum OpenACS Q&A: OpenACS 3.x reads .html files into a TCL string, TCL 8.x uses Unicode
Henry Minsky's AOLserver patches that explicitly set the OutputEncoding and so forth should solve this, at least for sites needing only a single character encoding (eg. Latin1) for the entire site.
I'll try to get an AOLserver 3.3+ad13 RPMset built that includes Henry's patches, and an nsd.tcl that uses the new parameters they provide.
BTW, it seems that this whole thing has been discussed before (ie. I am going over old ground here...!) -- I'd just not realized that the difference in handling .html files was directly related to the TCL 8.x stuff, until I actually read the code where OpenACS deals with serving .html files!