While Formstack for Salesforce does not officially support multiple languages, there are a few workarounds you can do to change the language of your form to match the language for your company.
Changing the Label
The easiest way to create a multi-language form is to change the labels of your fields to the language you desire. To change the label, you can either double-click on the label in builder mode or click the chevron to the right of the field to change the label.
If you have any questions about the above, do not hesitate to reach out!