The Modern Sidebar and Modern Footer can be translated using WPML.
To do this, go to the "Feast Layouts" section while on the primary language, and create a layout to assign to the sidebar and footer.
Then, change the language and create new pages to assign to the sidebar and footer for that language.
In WPML, you need to enable translations on the Feast Layouts custom post type.
In Polylang, you'll also need to enable translations on the Feast Layouts custom post type.
We don't recommend multi-lang blogs
Generally speaking we don't recommend running multi-language blogs. Why?
Traffic from non-U.S. countries earns much lower RPMs and sites can run into duplicate content or topical dilution issues if not structured properly. Additionally, you could do twice as many U.S.-focused english posts by not having to do twice the work by creating the posts in a different language.
All this means that you do more work for worse results than an English language site.
If you have more time and money than you know what to do with then this is a fine decision, otherwise, you should run an english-only site targeting U.S. traffic.