Adds german translations

[funkyfuture]

Motivation and Context

It makes the app more accessible to users with german as mother tongue. Also, a new section in the contributing doc may encourage users to add more translations.

How Has This Been Tested?

Installed in a project, checked the admin forms. Some of the strings didn't appear (and neither did the origins).

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have run the make format command to format my code
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-io]

Codecov Report

Merging #484 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #484   +/-   ##
=======================================
  Coverage   97.19%   97.19%           
=======================================
  Files          16       16           
  Lines         713      713           
  Branches       94       94           
=======================================
  Hits          693      693           
  Misses         10       10           
  Partials       10       10

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[rossmechanic]

Thanks for this @funkyfuture !