Well, about Openoffice.org. I don't know what you want. It's easy to just install the latest German version of OOo, rather than installing a language pack as an add-on.
OOo comes as .rpm, which sometimes leads to trouble on a Slack based system such as Vector, although I never did install OOo on Vector... but I expect the same troublesas in Slackware. Truckloads of unmet dependencies. Quatsch. Install with the --nodeps flag, or do as I do and <rpm2tgz *rpm> all the needed files (you don't need every file in the download and then <installpkg *tgz> and you'll be fine.
If you choose to install only a language pack, then I wish you luck ;-) I couldn't find a language pack for the same version as is in the default Vector install. But if you feel lucky, you might try this one
(<= Link to download)(Link to German OOo =>) Link
I don't know if xpdf has a localized version. No mention of it on the home page or ftp server, as far as I could see. But I'll confess that I did not look as thorough as I could have. Look here
if you want to delve into this deeper. Happy hunting ;-)