I see 2 problems.
1) You use self.INDEX in your recipe, but it is not defined.
2) I ran the recipe with that removed, and it found instances of pager:
Code:
pager = soup.find('a',attrs={'class':'nextPage greyButton'})
Where there was no <a> element with href attribute.
Until these are fixed, it won't work. The pager is a tag that includes what you need for building a link to the next page. It must only be found on pages that are multipage. You must find or create the link to next page (using INDEX plus href attribute or whatever) from pager. Pager must never be found on the last page of the multipage article (this tells it when it is done building the entire article).
I cannot read German, so can only guess at how to do this.