All files regarding i18n are now part of the PloneTranslations product, which
can be found in Plone Collective:

https://svn.plone.org/collective/PloneTranslations/trunk/

Additions to manual.pot now have to go in:

https://svn.plone.org/collective/PloneTranslations/trunk/i18n/atcontenttypes-manual.pot
