The first thing a translation team typically does is translate the po files for various applications. This allows the application labels and text to be displayed in a particular language.
General GNOME user documentation includes The GNOME User's Guide and the GNOME User FAQ.
Applications typically have application-specific manuals which are generally available from the Help buttons or menu. These tend to be the largest documents and thus require the most amount of effort.
We need to continue to improve this web page until it is reasonably mature.
We need to identify what documentation new translators need to make getting started translating easy.
We should consider what tools we need to make translation of documentation efficient (and even possible) in the future when the amount of GNOME documentation that needs to be translated and maintained becomes very large.