Language translations of vQuiz

Well, I obviously don't understand. But thanks for your time anyway. I;ll try to figure it out!

I told you.

This is only for the backend. Is there a way to change the language in the frontend?

The language files should be there: YOURSITEROOT/components/com_vquiz/language and there:
YOURSITEROOT/administrator/components/com_vquiz/language
Create here nl-NL or nl-BE folder, copy en-GB.* language files, rename it to nl-NL.* ones and translate what you want.

I don't know why vQuiz languge folders are inside component folders, but if nothing work you can copy language files to oficial places:
YOURSITEROOT/language
YOURSITEROOT/administrator/language

Or, you can create overrides in the Joomla backend: YOUSITEWWW.NL/administrator/index.php?option=com_languages&view=overrides

Select Dutch (Site) and go.