Hello!
Dutch is actually in the list. The code is NL.
If you are ok with the default messages (“survey already answered” or “unavailable”) you don’t have to do anything because Qualtrics already have translation for those messages.
Now, if you want to customize those messages, you need to follow the instructions here to translate them to the languages you need. For that, you need to create the original message in French (FR) and then add the translation to Dutch (NL) and then update the messages in survey options.
Also, you need to create the translations for other messages like invite, subject, reminder, etc. The process is exaclty the same.