Edge UI: Use browser Language as Default

[da-Kai]

• Fallback to browser language when AuthenticateResponse provides no language.
• Centralize logic for retrieving the current language
• Change default Language from de to en
• Replace Fenecon specific no local history notice with a generic OpenEMS version.
• Set language explicitly to de in Karma tests.

Address language issue in #3411

[codecov[bot]]

Codecov Report

:x: Patch coverage is 37.03704% with 17 lines in your changes missing coverage. Please review.

:x: Your patch check has failed because the patch coverage (37.04%) is below the target coverage (75.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #3415      +/-   ##
=============================================
- Coverage      59.60%   59.60%   -0.00%     
  Complexity       112      112              
=============================================
  Files           2922     2923       +1     
  Lines         126328   126334       +6     
  Branches        9412     9401      -11     
=============================================
- Hits           75285    75284       -1     
- Misses         48185    48197      +12     
+ Partials        2858     2853       -5     

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