magento2: The front-end date-picker is not localized.

The front-end date-picker is not localized: days short names are all in default en_US.

Preconditions (*)

1. Magento 2.3.x & 2.4-develop
2. Date format used is “E, dd.mm.yy”
3. Create a store view ( German - de )
4. From Stores > Settings > Configuration > General > General > Locale drop down , assign language ( German (Switzerland) ) to the created store . ( Scope : German from top left drop down )

Steps to reproduce (*)

1. Run:

composer require community-engineering/language-de_de
php bin/magento setup:static-content:deploy de_DE
php bin/magento indexer:reindex
php bin/magento cache:clean
php bin/magento cache:flush

1. Admin > Settings > Configuration > Customer > Customer Configuration > “Show Date of Birth: Require”
2. Login and switch to German store (de) and edit your account and use the datepicker of the DOB field.

Expected result (*)

Days ( Short name ) are translated to German ( Ex in de_DE store)

Actual result (*)

Days ( Short name ) are in English.