Update documentation for translators

[rmol]

Status

Ready for review

Description of Changes

Updated documentation for SecureDrop translators, adding instructions for dealing with HTML content and guidelines for resolving differences in translations. Also updated screenshots to match our current version of Weblate, and eliminated the copied EFF glossary entries, instead linking to their full glossary.

Fixes #4624.

Testing

Check out this branch, run make docs and browser to http://localhost:8000/development/l10n.html to review the changes.

Deployment

Documentation only.

Checklist

If you made changes to documentation:

• Doc linting (make docs-lint) passed locally

[codecov-io]

Codecov Report

Merging #4719 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #4719   +/-   ##
========================================
  Coverage    82.23%   82.23%           
========================================
  Files           48       48           
  Lines         3350     3350           
  Branches       380      380           
========================================
  Hits          2755     2755           
  Misses         503      503           
  Partials        92       92

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[kushaldas]

Looks good to me, and nice screenshots :) @rmol