We did something similar for our client who wanted the landing pages in five different languages on the website.
While making the form, you have the option to select the language for the form. So, you can just select French and make your form.
For landing page, I suggest you make all the content in a MS Word document in French language. You can then import the French font in .ttf and .otf format in your assets. After that, you just need to include that font in your code and simply copy and paste the content in the landing page.
Let me know if this fulfils your requirement.