We use a native functionality (form input type 'datetime-local') of the browser to show the date picker, and therefore, this needs to be customized at the browser level.
Go to Chrome Options (3 vertical pips in the top right-hand corner)
Choose Settings.
Click on Languages
Click Add languages and find your location-specific language e.g. English (United Kingdom) and click on the 3 vertical pips beside the language you just selected
Then click on Display Google Chrome in this language
Restart Chrome.