With this patch the German PDF manual has no more encoding problems.
This should go to core-updates or a new texlive-upgrade branch, because
it results in countless rebuilds.

There are still remaining problems when using make doc/guix.de.pdf:

* kpathsea causes mktexpk to be run for a number of fonts that already
  exist in the union (e.g. ecrm1200).  Why aren’t they found?  Perhaps
  that’s because TeX Live only includes the font metrics (.tfm), but not
  the .pk files.  I wonder why the .pk files are used at all.

* despite successfully generating the PDF file in the temporary build
  directory, make aborts:

  /gnu/store/mw4llmn2l617gf5zakfk1l154f19lxbm-profile/bin/texi2dvi: pdftex exited with bad status, quitting.
  make: *** [Makefile:4375: doc/guix.de.pdf] Error 1

Why?

-- 
Ricardo