German translation: Initial translation (draft)

[janezd]

Add German translation, fix import paths for localization module..

Possible problems (among others):

• Bad translations, e.g. bad wording, a different word used in translation.
• Incorrect translations of code in f-strings, e.g. translated variable names, incorrect calls of plde.
• "Strings" that must not be translated. These were marked as "must not be translated" in the Slovenian translation, which is used as template, but I could have missed some. E.g. in open(..., error="strict"), I did't mark "strict" as non-translatable, and in the German translation it was translated to "strikt".

The first problem causes embarrasment, the latter two cause runtime errors.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.04%. Comparing base (600f194) to head (c11d0a3).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #287   +/-   ##
=======================================
  Coverage   72.04%   72.04%           
=======================================
  Files          34       34           
  Lines        9115     9115           
=======================================
  Hits         6567     6567           
  Misses       2548     2548           

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