Yes, you can build your own landing page that displays your own custom content in any format and in any language. You just need to build your own HTML code and store that in SendGrid by following the instructions below.
You can log into your SendGrid account by using the credentials provided to you.
Click on Settings -> Tracking -> Subscription Tracking as depicted in the following picture.
You can create your own unsubscribe landing page content by entering your own HTML code to create the landing page.