To start a new translation, the most simple way is to copy the
existing POT as article.lang.po, where lang is your
language code. For example, to prepare for a new translation of the
essay https://www.gnu.org/philosophy/free-sw.html, you can
cd philosophy/po; cp free-sw.pot
free-sw.lang.po and then edit the latter. If
free-sw.pot does not exist it is because either the article is
not yet “templated” (i.e. migrated to the new style), or the GNUN
maintainers have not yet added it to the value of the appropriate
variable in server/gnun/gnun.mk. In that case, just ask them
to do what’s needed for the POT to be generated.
You could also use the
msginit utility that would populate
the PO file header with the right information, provided your
environment is set up correctly. See msginit Invocation in GNU gettext tools.
GNUN also provides a customized script to automatically fill more header fields. See gnun-init-po.