The wording of the GDPR texts is translated (into Dutch), but the title still says "Terms and Conditions". Where to find the string to translate? Or how can it be translated? Please include a translation in next releases. It's odd on an event registration in local language to speak about "Terms and Conditions"!
Currently the string in question isn't properly translated into Dutch.
CiviCRM's translation project(s) live on Transifex. There are two "teams" (to use Transifex's nomenclature!) for translation.
Within each "team" the translations are broken down into "resources" - groups of strings. For core these are functional areas of the software. For extensions it's a single resource per extension.
The GDPR extension is setup on Transifex for translation under the extensions team and having checked there is some progress that could be made to achieve a more complete translation into Dutch.
Simply register on Transifex and use their somewhat clunky UI to translate the strings - then they will be automatically built into .mo files by a nightly job and will soon be available to use in CiviCRM.
Hope that helps!