Default Python charset is 'utf-8' only for version 3 as i found in many
documents.

I was trying to investigate roundup code and remove various decode and
str(). But then error appears in different place and when it was on
_socket_op(self.request.wfile.write, str(content)) in client.py i gave up.

I don't fully understand a conception of charset handling in roundup. 

Things, like 
- client.py (write_html)
        if self.charset != self.STORAGE_CHARSET:
            content = content.decode(self.STORAGE_CHARSET, 'replace')
            content = content.encode(self.charset, 'xmlcharrefreplace')
- engine_jinja2.py (render)
        return self._tpl.render(c).encode(client.charset, )

are implying that all output will follow a client preferred charset. But
roundup templates prepared by a roundup administrator usually contain
predefined ' <meta http-equiv="Content-Type" content="text/html;
charset=X">' in they content, as seemed to me.