Plural forms not imported into Drupal 5.22 core

Hi,
First of all sorry if this post is in the wrong place, am finding the whole localization thing slightly confusing ;)

I was looking for a Drupal core 5.22 translation... the translation page on d.o tells me to look on localize.d.o but that tells me to look for language projects on d.o....

Anyway I eventually went into http://ftp.drupal.org/files/translations/5.x/drupal/ and downloaded drupal-5.22.de.po, which I uploaded into my Drupal 5.22 site using the Localization import language feature. However, none of the plural forms gets translated (user/s, day/s), nor its single form.

However if I use the language pack http://drupal.org/node/576740, which has the multiple .po files, and if I import modules/system/translations/includes.de.po then some of these plural forms get fixed.

BTW should I be using http://drupal.org/project/autolocale to ease the pain of import all the entire language pack files?

Thanks!