Enable switching translation language and update locale messages

[JohnMwashuma]

Fixes #371

Task check list:

---

• [x] Make LANGUAGE_CODE configurable.
• [x] Update locale function to the following:

  def locale(request):
  locale = request.session.get('locale') or getattr(
      settings, "LANGUAGE_CODE", None)
  if locale and translation.check_for_language(locale):
      translation.activate(locale)
  return {"locale": locale}

• [x] Make sure all magic strings are wrapped in translation.
• [x] Remake locale messages using python manage.py makemessages -l ar
• [x] Translate the msgid property inside the django.po file where the msgstr is msgstr "" to Arabic and recompile the messages using python manage.py compilemessages
• [x] Make datatables language definitions dynamic based on the current locale/language code.
• [x] Fix failing tests
• [x] Add linting pre-commit hook

Related to:

---

https://github.com/onaio/infrastructure/pull/6938

[codecov-commenter]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@740470e). Click here to learn what that means. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #377   +/-   ##
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  Coverage          ?   66.91%           
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  Files             ?      123           
  Lines             ?     7533           
  Branches          ?        0           
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  Hits              ?     5041           
  Misses            ?     2492           
  Partials          ?        0           

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[JohnMwashuma]

Codecov Report

exclamation No coverage uploaded for pull request base (master@740470e). Click here to learn what that means. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #377   +/-   ##
=========================================
  Coverage          ?   66.91%           
=========================================
  Files             ?      123           
  Lines             ?     7533           
  Branches          ?        0           
=========================================
  Hits              ?     5041           
  Misses            ?     2492           
  Partials          ?        0           

mega We’re building smart automated test selection to slash your CI/CD build times. Learn more

The warning No coverage uploaded for pull request base is because codecov is not running/configured on master yet.