language problem since update

Hi,

Since our most recent update of WordPress and plugins we have a problem with some of the text no longer being displayed in Dutch (but in English). In particular the details added under every single event.
After searching the forum I found someone with a similar problem and a solution that said something about downloading new mo & po language files.
But I cannot find where to do that (the provided link in that post gave a 404).

Not sure if this is the solution I need, or if something else is them matter. But I hope you can help me!
Thanks in advance.

additional info: I do use edited templates, could it be that they no longer work correctly with the newer version of the template?

https://wordpress.org/plugins/the-events-calendar/