The files that are to be translated by the individual languages teams are stored in the following locations:
The original GUI translation templates are located in l10n-kf5/templates/messages.
The already translated GUI files (the POs) are located in
For the procedure on how to make a PO file from POT file please read the section on GUI translation.
The translated documentation files are located in
l10n-kf5/. (The same goes for downloading these files as for POs.)
For more info on this whole subject please read the section on doc translation.