Hello.
Not sure but I think you can customize the messages from List Building (dropdown menu) > Unsubscription and changing the languages.
Here you can find the documentation page with more info on the cancellation process https://www.thenewsletterplugin.com/documentation/cancellation .
I would like to add a question to this topic: To change the email style, can I directly add custom CSS code editing the messages under “Text” instead of “Visual” and adding the <style> tag?
Hi, every single message or label can be translated from the subscription, unsubscription, profile or form fields panels. Usually most of those message should be loaded in your blog language if the blog download the translations from WP.org. You can try to use the reset button on those panel to reload the messages.
We have not a cancellation form, the cancellation starts always from newsletters you send.