I managed to create an updated po file. Steps:
create an empty pylons app.
paster create --template=pylons dummy
copy dummy/setup.py to your rhodecode-egg directory
excute python setup.py make_messages -o yourlanguage.po
move yourlanguage.po to a new dir in i18n/yourlanguage/LC_MESSAGES/
Then use poedit to edit yourlanguage.po file. When saving poedit will create a compiled filed named yourlanguage.mo.
Go to production.ini and change language setting to yourlanguage.
Caveats: this method doesn't extract many strings in templates, I'm trying to fix this.
But, you can add manually with a text editor this strings (not with poedit).
The enhancement would be to distribute a full localizable strings template file rhodecode.pot.