This is what I did to integrate de.po from http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=507867 and http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=510158. The key tools are msgmerge and msgfmt.
cp de.po nmap/zenmap/share/locale cd nmap/zenmap/share/locale msgmerge -U de.po zenmap.pot
Edit de.po to remove obsolete strings (lines starting with #~) and fuzzy translations, unless there's an obvious easy way to update the fuzzies.
mkdir -p de/LC_MESSAGES msgfmt de.po -o de/LC_MESSAGES/zenmap.mo svn add de.po de
Test it.
cd ../../.. LANG=de_DE ./zenmap

Screenshots in other languages: de fr hr pt_BR ru.