Hi,

Regarding your original language, you can switch from EN to NL. However, to make it work, you will have to switch all your website content in Dutch otherwise you won't be able to translate into English. Indeed, the original language is the one you choose to build your website and can't be anything else.

Note that if you want to do this to redirect Dutch users to the Dutch page, Weglot provides the 'auto-redirect' feature that automatically redirects the visitor to his language, based on his browser's language.
Once you activated it, visitors will be automatically redirected to their own languages (if selected in your destination languages). However, if you don't support the visitor's language, he'll be redirected to the original language of your website.

Don't hesitate if you have any other question.
Regards,