Sphinx
Sphinx has gettext support:
http://www.sphinx-doc.org/en/stable/intl.html?highlight=gettext
Lektor
The upcoming new Tor website uses Lektor.
There's a PO plugin for Lektor but Tor does not use it. Ask hiro for details.
Lektor will soon be in Debian.
Hugo
See Birger Schacht's PoC conversion.