@toerfiets: Hello Hans,
To translate the plugin in Dutch you will need to follow the steps below.

First of all you will need to use Poedit software. Install and Open the software.

Create New Translation => Browse and Select catch-instagram-feed-gallery-widget.pot file from the languages folder and Click Open => Select the language as Dutch.
Now, you will see a list of translation ready strings and Translation text area where you can add the required translation. Search for the strings you want to translate and add the translation. When you are done translating the strings save the file to the languages folder.

Now,Go to => Dashboard => Settings => Select Site Language as Nederlands and Save Changes.

You can email me the translation file after you are done so that we can bundle it in the plugin folder itself.

Do want the footer instagram to be there as it is and have another instagram feed below the featured content or do you want to change the position of the footer instagram widget?

Let me know if this helps you out!
Kind Regards,