How to translate calendar signs

Hi everyone,

I have a little problem to solve. I’m building new multi-language website for hotel and I’m using this plugin for reservations. In this case is very useful date-type input which opens up a calendar. But I need to translate signs of moths and days for every language version of the site.

In one weather plugin, there were an option of adding filter to functions.php, where I was able to rewrite particular words from english to needed language. Is there any chance to do the same here?

Thank you very much

http://wordpress.org/extend/plugins/formbuilder/