hello, nice to see this project. it appears that you a multilingual 4 page website with 2 contact form. I have read the detail for the contact form with check box, multilingual plugins, German and English language, seo friendly, installation, testing etc. I have gone through the documents in zip attached.
I have built multilingual websites in the past with contact forms. I have built responsive, attractive, seo friendly, user friendly, easy to edit websites with complete testing and installation on client server. I can share the references of my websites. It appears to be an interesting job as per my experience. Looking forward. tx