On my system "make update-po" still comments out very many msgids, e.g. "intro_sentence1". Could you double-check if this happens on your system too?
"intro_sentence1" is not commentized on my computer, but I use the revision with the source. You may have a problem if you use the binary release: make update-po search inside *.c code files AND inside *.ufo files for any msigs appearing in game. Therefore, if you don't have the source files, every msgids coming from those *.c files will be removed (you'll have only texts coming from *.ufo files).
The quality of the German translation in the 2.2 release was so low that it hurt sometimes. In the last days I fixed many German translation errors in the Wiki. I just want to have them right now in the game. I do not feel like waiting until the next release. ;-)
If you just want to update the german translation for 2.2 release, you don't need to use "make update-po": I used it just before releasing 2.2, so msgids are up-to-date.
All you need to do is:
1. Fix the translations with poedit in de.po
2. in the folder containing the ./ufo executable file, just type "make lang" to compile the new translation.
And that should be enough to have your new translation in game.