Calendar Language

Hi, I had this problem a year ago when using this plugin but was not able to fix it in time, now I need the plugin again and am having the same problem!

Every part of the plugin display is in English except for the calendar month and days of the week – which are in a different language! I have searched up and down in the settings but can not find a way to change it to English. I tried removing the plugin and reinstalling, which worked at first, but once I customized the fields of my form and saved the settings it reverted to the other language.

I would deeply appreciate any help!

The page I need help with: [log in to see the link]