Guidelines for Developers
An overview on how to enable i18n in your Plone Product.
(not written yet)
You'll find some directions on http://dev.zope.org/Wikis/DevSite/Projects/ComponentArchitecture/ZPTInternationalizationSupport in meanwhile.
Also, there a how to on http://plone.org/documentation/how-to/i18n-for-developers
Additionally in Plone 2.5 a new technique to i18n-ize Python code has been introduced. See the corresponding PLIP 108 for a detailed explanation.
And a short FAQ about overwritting Plone's translations with customized ones http://plone.org/documentation/faq/keep-translations-separate