Then I checked if there was an update for the translation available, but when I refresh the page after performing the update I get the same message. So I can keep running the update endlessly.
@CD130 The Update Translations page is for the translations of the admin interface and updates the database. The files in the texts directory are for the front-end (public) pages and are updated only in a new release of phplist.
You can either update the dutch.inc file directly, or create your own file that contains any missing translations and place that file in the web root directory.
e.g. create file dutch.inc in the web root directory then add the missing translation
<?php
$strForwardForwardingName = 'Please enter your full name';