The German translation is reasonably complete. Please check if the partner who you are sending the quotation to has his language set to German too. That will trigger the labels you mention.
If there are still words that have not been translated (there are...) or that you want to have translated differently, then go to 'Settings'>'Translations', search for the word to be translated and change to you liking.

Hi there,

i was actually takling about the pdf-quotes (and invoices). Sorry for being not clear. But in pdf-Quotes there seems to be no way to change these labels.
Under 'Settings'->'Translations' I can only 'load a translation'

Do I miss something?

I'm currently evaluating Odoo for two different customers in German-speaking countries.

Odoo is, in fact, not translated to a sufficient degree, yet. It's (by my totally subjective estimate) ~80% complete at best and can be very spotty and seems to be clumsily done (i.e., not by a native speaker).

Maybe set up a community translation system?