Partly translating the site’s text in the unified site settings allows you to change the text of some site elements in one place. For now, it is possible to edit the thank you pop-up displayed when sending a submission via a contact form. And, if you have a multilingual site, you can set separate texts for each language version.

Open Site settings, go to the Multilingual site section, and a little lower is the needed Translate parts of the text on the site section: