@rbf: Hello Nynke,
To translate the strings in the theme first of all you will need to use Poedit software. Install and Open the software.
Create New Translation => Browse and Select gridalicious-pro.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.
But I suggest you to create a child theme before doing all this as when you update the theme to the newer version the translation you added will be lost or what you can do is you can translate majority of the strings available for translation and email it to me and I shall add it to the theme itself with your name as the contributor.
Let me know if this helps you out!
Kind Regards,
Skandha
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