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;
- Put the Language Selector widget on the page and choose 中文-中国.
- Click on the Date field so the Date Picker can appear.
The weekdays shows "S 月 T W T F S".
The weekdays shows "日 一 二 三 四 五 六".