You are wanting to change the text on the button from "Register" to "Order" or something like that? Well, the text on the button is actually part of the image. There is no code or language file change that will modify the button text. You have to modify the actual image.
Inside of the DT Register package, there is a zip file with source image files... each of the button sizes in each available color are there with NO text. So you can add the text you need, then save the file as the EXACT same filename as the original and upload it over top of the original file here: