There are mainly two ways to find out which programs have not been translated yet:
Try to figure it out from the KDE internationalization status table.
Compare the POT files with the POs for the particular language. In other words: If there are no PO files for a particular program under "l10n-kf5/
package-name" then the chances are pretty good that the program has not been translated yet. (This comparison is done automatically by the "Project Overview" of Lokalize, by the way.)
However, before translators jump right in, it is probably a good idea to ask their team coordinator whether a program is not being worked on by someone else and to make sure that the program is not being rewritten or replaced by another one. To-do lists for your team and a system of "package maintainers" (people who are responsible for the translation of whole KDE packages like kdeutils, kdemultimedia etc.) can also often be a big help in avoiding duplicate work.
KDE programs are constantly improved. The downside to this rapid development is that almost all GUI texts are constantly changing and the translations are just as constantly in need of revisions. To find out which already-translated programs need a revision, either SVN update your working directory or refer to KDE's GUI messages translation statistics.
The above mentioned statistics page organizes the information at three levels: SVN branch, translation team and package. At the package level you will find detailed information about the amount of fuzzies in each .po file. The .po files with fuzzies are the ones in need of a revision. "Fuzzy" is like a kind of question mark for the translations. These are sections which have been marked by an automatic checking routine (in msgmerge) as "suspicious" which means something to the effect of: "Please check this translation again because the original has changed".
An overview of how the language teams are doing is provided on the Translation statistics by team for trunk branch. Based on the percentage of translated messages the decision is made which languages will be part of a KDE release and which are not. (Normally, around 90% of frameworks and around 75% of kde-workspace should be translated in order to get into a release.)
When the essential requirements will be met, you should send a message about this at
(kde-i18n-doc AT kde.org) (but please do not attach translated files to it) to obtain further instructions.