Give the doc toolchain a way to create PO files, and generate translated XML files from them.
Translators generate PO files with 'make po', then enter translated strings with poedit or the like. After enough strings have been translated to make a useful document, 'make tran' is used to generate the translated DocBook XML file from the PO file.
Translators commit their PO files, and the generated XML is only used temporarily for creating the final output format.
devel/gettext-tools and textproc/itstool are required. These will be added as dependencies to textproc/docproj.