I believe this is the shortest description ever about the process of translating GNOME to Brazilian Portuguese. For more information, read our project page (in Portuguese) or drop by the #tradutores channel at FreeNode.net.
GNOME has a SVN repository where each module is more or less a program (e.g. Evince). The module contains source code, translation, documentation, documentation translation and whatever else might be related to that program. The mesage catalogs keep the same unless we touch it, but the GNOME translation statistics site provides a convenient interface where “regular” translators can download the catalogs. In this site the message catalogs are automatically updated to reflect the strings in the source code. The documentation is (still) in DocBook format, but GNOME has tools to create a POT file from a XML one, and during build time this tools convert message catalogs to translated DocBooks. Selected people have access to the SVN repo, but our translation team entry barriers are so low we don’t even know how many translator we have at any given time. We just ask people to say hello in our mailing list and read our documentation. When a translator wants to translate something, he puts his name besides the chosen module at a particular wiki page.