Hi,
Thanks for using the Events Calendar.
Here on the pre-sales forum, I’m afraid we do not provide technical support. I would ask that you take any technical support questions across to our wordpress.org forum – our staff scan it periodically and other community members may also be able to help out.
The Events Calendar
Having said that for now the plugin only looks in the /lang/ directory and will be overwritten on updates.
In 4.2 we are adding a feature where you can put them in this directory:
wp-content/languages/
So look for that on the release of 4.2 in a couple months.
Thanks again!