STEPS TO REPRODUCE
1.- Instance a search portlet on a page
2.- Search for any word. It does not matter
3.- Go to "Custom Range..."
4.- Click on "From" to display the calendar
5.- Change the URL to request that page again in a different language, for example Spanish
6.- Click again on "From"
The calendar is displayed with its words for the months, the days and the day order in English
It should be displayed in Spanish