[stable4.5] simpler locale fall back code

[backportbot-nextcloud]

Backport of #5418

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (5c15b6b) 22.63% compared to head (8a4969b) 22.64%.
Report is 1 commits behind head on stable4.5.

Additional details and impacted files

@@             Coverage Diff              @@
##             stable4.5    #5466   +/-   ##
============================================
  Coverage        22.63%   22.64%           
  Complexity         395      395           
============================================
  Files              241      241           
  Lines            11834    11830    -4     
  Branches          2299     2299           
============================================
  Hits              2679     2679           
+ Misses            9155     9151    -4     

Flag	Coverage Δ
javascript	13.84% <0.00%> (+<0.01%)	⬆️
php	64.26% <ø> (ø)

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Files Changed	Coverage Δ
src/utils/moment.js	0.00% <0.00%> (ø)

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