Well, your problem is that you use multi-site for translations in the first place.
I strongly suggest Polylang for translations as it’s more reliable and doesn’t require that much maintenance.
In your case I suggest you use Yoast or a SEO plugin that allows you to control the indexing status of your post/cpt or individually per post.
Basically, you just set the meta robots to noindex
<meta name="robots" content="noindex">