The files that are to be translated by the individual languages teams are stored in the following locations:
The original GUI files (POTs) are located in kde-i18n/templates (get them via CVS, CVSUP, WebCVS, or ftp)
The already translated GUI files (the POs) are located in kde-i18n/language/messages (you can get them the same way as the .pot files; besides there are separate packages for the individual languages from the i18n server)
For the procedure how to make a PO file from POT file please read the section on GUI translation.
The original documentation files (in SGML format) are stored in with their respective packages (kdebase, kdeutils etc.)
The translated documentation files are located in kde-i18n/language/docs (as for downloading these files goes the same as for .po files)
Attention: the documentation files are being converted from LinuxDoc to DocBook format right now (both kind of SGML subformats or "DTDs" which is short for "Document Type Definitions"). There may be still some files in LinuxDoc (or HTML) format around: do not touch these, esp. do not translate them.
For more info, read the section on doc translation.