Read this Translation HOWTO entirely, especially the section on GUI translation in KDE.
Find out how to install KDE and then just do it. Although you can theoretically do your translation work for KDE under an older version than the one the translation is meant for, it is better and recommended to have the needed version on your computer for at least testing purposes. Check out the HOWTO section for assisting documentation on this subject.
Make sure you have the GNU gettext package installed and start to get familiar with it. You have to install version of gettext >= 0.17. At least have a good look at its Info pages. (Remember: the KDE on-line help provides a very convenient way to read this kind of documentation.)
Take a closer look at the programs, scripts and statistical aids which will help you with translation. You will need programs and tools that can handle the UTF-8 encoding, at least for the GUI translation. The recommended tool for making translation is Lokalize.
In case you have never heard of SVN (in full: Subversion): it is a version control system for directories and files. In the case of KDE (as for many other open source projects), it is used so that files and directories may be created, modified and removed by different users over the Internet. In KDE, the name "SVN" or "KDE SVN" primarily refers to a server called "svn.kde.org" where the translations for KDE are stored. People with a SVN account have a local client setup on their own computer corresponding to this SVN server which creates local working copies of the source tree on the remote machine. This local SVN client also allows them to merge e.g. new translations back into the remote source tree system.
If your team reaches the essential requirements or there is the need in committing files by yourself, you should apply for commit account. Please see the tutorial for how exactly to do it correctly.
It is suggested that only the team leaders have commit accounts, but, of course, it can be more than one if your team needs them.
If you do not know SVN, or if you do not know it well, probably you want to read the handbook about SVN, which is available online: Version Control with Subversion, it might be part of the documentation of SVN packages that you have or are going to install on your system. (The book is also available as "hardcopy" in bookshops). Of course, as you will only use SVN and as you plan neither to program nor to administer SVN, you do not need to read and understand all chapters of the book.
The main commands of the svn client are: svn checkout (for getting something from the remote system to your local repository), svn update (if you just want to refresh already existing stuff on your local system), svn add (to add new files and directories as being), svn remove (to remove new files and directories as being), svn copy (to copy files), svn move (to move files) and last but not least: svn commit (to "register" your work back in the remote system. This is a process named "committing").
Among other graphical front-ends we mention kdesvn. There is also the svn: KIO slave (part of the kdesdk-kioslaves project), which gives some SVN functionality, for example in Konqueror, Dolphin, and KDevelop.