Some users that use the International version of Nintex forms, use to show the designed form on the Nintex Form Web Part.

On those cases when a user saves a form, they see the following message: "Item added succesfully" , that is not a message in their language.

Here is a workaround so as to change that message:

Add the next sentece on the Form settings, custom Javascript section.

NWF$("span:contains('Item added successfully')").html('Vare tilføjet med succes');