Add fallback locale

[dominik-zeglen]

I want to merge this change because it fixes some bugs causing locale to be undefined, which would make <DateTime /> components explode.

Pull Request Checklist

1. All visible strings are translated with proper context.
2. All data-formatting is locale-aware (dates, numbers, and so on).
3. Translated strings are extracted to .pot file.
4. Number of API calls is optimized.
5. The changes are tested.
6. Type definitions are up to date.
7. Changes are mentioned in the changelog.

[codecov]

Codecov Report

Merging #153 into master will decrease coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #153      +/-   ##
==========================================
- Coverage   74.45%   74.44%   -0.02%     
==========================================
  Files         507      507              
  Lines        5062     5063       +1     
  Branches      866      867       +1     
==========================================
  Hits         3769     3769              
- Misses       1153     1154       +1     
  Partials      140      140

Impacted Files	Coverage Δ
src/components/Locale/Locale.tsx	33.33% <0%> (-2.39%)	⬇️

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