feat: add localization and transifex support

[fsbraun]

Description

This PR adds localization and transifex support.

• Transifex config is found in .tx/config
• German and English localization files are added (more to come from transifex)
• Quotes in three templates adjusted so that ./manage.py makemessages --all creates the correct strings

Related resources

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Checklist

• [x] I have opened this pull request against master
• [x] I have added or modified the tests when changing logic
• [x] I have followed the conventional commits guidelines to add meaningful information into the changelog
• [x] I have read the contribution guidelines and I have joined #workgroup-pr-review on Slack to find a “pr review buddy” who is going to review my pull request.

[codecov[bot]]

Codecov Report

Merging #305 (648dfd1) into master (f13e299) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #305   +/-   ##
=======================================
  Coverage   89.75%   89.75%           
=======================================
  Files          67       67           
  Lines        2196     2196           
  Branches      293      293           
=======================================
  Hits         1971     1971           
  Misses        170      170           
  Partials       55       55           

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