Steps to reproduce:
- Create a new Form with a Date field and publish it;
- Add a Form widget on a page and select the newly created Form to be displayed;
- Change your display language to any other different than English (you can do so by putting the Language Selector widget on the page and choosing the language from it);
- Click on the Date field so the Date Picker can appear.
All the months in the month drop-down and the weekdays' initials are still in English.
The months and weekdays should be translated according to user's language of choice.