DanCoulter

Once activated, this plugin will translate every instance of the jQuery UI 
Datepicker plugin on your blog. It even comes with the latest version of 
the jQuery plugin, so that you can add it to pages on your blog.
This will only work with version of the Datepicker plugin that come with 
jQuery UI versions 1.5 or higher.

Datepicker i18n

Globally translate your jQuery UI Datepicker instances.

kamiel79

WordPress has the function wp_localize_scripts for translation, but the strings passed to it have to be hard-coded. Until you parse the .js-files and scan for occurrences of _e() with a fast regexp, and localize them with the data using the WordPress _e-function to localize from a .po file. *Note*. Your po-file has to include strings from javascript files. To do this in Poedit, see http://stackoverflow.com/questions/16557327/how-to-generate-po-file-from-js-file-using-poedit.

Localize js

Provide translation function _e("") in javascript files.

Datepicker i18n vs Localize js