Wanting to get the jQuery UI Datepicker rendering the calendar in different languages? Already got jquery_update and seen the files like jquery.ui.datepicker-de.js in jquery_update/replace/ui/ui/i18n with the translation of the month and day names? Think you need some custom code to utilise those files, maybe by performing a drupal_add_js()?
No! The locale module already has an integration with Datepicker so assuming you are using that, all you should need to do is translate the English month and day names into your desired languages via the standard string translation interface.
If you invoke the jQuery language file(s) via drupal_add_js() it may appear to work, in fact you may be fine, but if you also have an AJAX form on the same page as the date picker, the AJAX processing re-triggers the translation of the locale module and if you haven't translated the month and day names, your calendar text will mysteriously revert back to English until you perform a full page refresh, upon which you will see the translation again.