Hi nicekicks,
Generally, The Events Calendar will use whatever language you have specified under the WordPress General settings. However, we don’t have a translation file for en_GB because no one has ever volunteered to make one. We’d love to have you make one, if you’re willing. Then you could set you site to en_GB and have the calendar use it too. I’d be happy to give you a 30% off coupon for the plugin of your choice in exchange for your work.
Check out the Getting Started post where you’ll find the instructions and files you need to do that.
Best,
Leah