Currently, localizations are available for the following languages: English (en,en_GB,e_US), Spanish (es), German (de,de_DE), Dutch (nl), Hebrew (he), Polish (pl_PL).
You can add your own localization, by creating a local copy of platform's 061-popcalendar.js file (copy it from <studio installation root>/plugins/tersus.appserver_<version>/DefaultWebapp/scripts to your application's web/scripts folder, and edit it to add your localization.
You can of course edit the file in it's original location, which will affect all applications running with that copy of the studio, but your localization will probably stop working once you update the studio to a newer version.
If you share your localization with us, we shall consider including it to the platform, so that there's no need for the local copy. You can attach the file to a reply (don't copy/paste ... use the Add an attachment button instead).
For best results, use the Firefox browser..