Language translations of vQuiz
The language files should be there: YOURSITEROOT/components/com_vquiz/language and there:
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:
Or, you can create overrides in the Joomla backend: YOUSITEWWW.NL/administrator/index.php?option=com_languages&view=overrides
Select Dutch (Site) and go.
What about open transifex project (for ex. www.transifex.com/wdmtech/) so we could collaborative translate language files to other languages.
Obviously, such a job for you is an overload of resources. So, teamwork is a real way to get a bunch of language translations.
I'm making russian translation by myself, but I could add my files to the common cause.