By default, Django describes the charset of HTML pages in the HTTP headers: Content-Type: text/html; charset=utf-8
With render_to, the mimetype is just 'text/html' by default, which means (as a French accents user) I have to redefine mimetype each time I use render_to, which is inconvenient.
I suggest defaulting 'mimetype' to None instead, which is what Django otherwise does (cf. render_to_response source code). This allows to reuse Django's defaults.