Jeroen,
Okay there are two setups you can do here.
Deploy WordPress multisite, then configure domains or directories like this.
Yourwebsite.com → English
YourWebsite.fr → French
Or if you don’t want to purchase domain, then make directories like
YourWebsite.com/fr → French
The French website will be copy of English one. We can just change the language on .fr domain to French right from the admin settings.
You can manage both the websites from your WP Multisite Admin. Those who want to work on English website can work on that.