Hi Franka,
When you change the default language in General Configuration, any members who are already registered in the system will need to update their account if they want the new default language.
You said when you changed your account language, the first sentence changed to Dutch. That’s great! And that’s expected behavior.
The reason the rest is still in English, is due to the fact that the language for that text comes from Freeform’s language pack and not ExpressionEngine’s.
On line 443 of lang.freeform.php, which is located inside the FreeForm module package, you’ll find this language here.
So ExpressionEngine is translating everything it can into Dutch, and in the case of this particular message page, Freeform is providing some of the language as well, which is still in English.
Does that make sense?
Let me know if you have any more questions.
Thanks!