I had trouble reading your summary, but I gather that this works best:
in the page header, plus this instruction to FormMail:
<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
And that the only problem is with the email headers (From and Subject, specifically).
<input type="hidden" name="mail_options" value="CharSet=ISO-8859-1" />
If I've understood the situation correctly, then the problem is twofold:
- The content-type inside an email does not affect the header fields. That's the way the email standard is specified.
- The email standard does specify a way to handle international header fields, but FormMail doesn't yet have that feature.