HOWTOs and Info Sites
The following seem particularly useful in the process of KDE translations:
Version Control with Subversion (The book is part of SVN, so it might have been installed on your system as part of SVN's documentation.)
The Build from source at community.kde.org
Live images provided by KDE Neon
Various information, especially lots of useful stuff on DocBook in general and KDE documentation in particular in the KDE Documentation Primer.