ABPro 3.0.5 uses the JQuery Datepicker.
As it is JQuery, it has no knowledge of Joomla or Joomla Language files.
ABPro ships with several translations included..
The translations are placed in the /datepicker_locale folder of the ABPro component.
Instructions for making translation files for other languages.
The jQuery Datepicker translations master list is here..
The link on that page is actually to a html page describing the .js file not a usable .js file.
To make a translation file you need to cut&paste the js code into a new file in the ABPro /datepicker_locale folder.
For example to make a Norwegian language file you would create a file called datepicker-no.js in the ABPro /datepicker_locale folder.
Cut & paste the Norwegian translation js code into the new datepicker-no.js file.
Now ABPro will display Norwegian datepicker.