The problem is, when I register a user on a site, it registers on all sites of the network and that is just completely ruining the idea of having different site languages on a multisite install.
No. When you register a user on the network they’re a user on the NETWORK. Check. Are you 100% sure they’re added as a user to all the sites? I bet they’re not unless you have some other plugin that does that. Because, while confusing, it’s not the same thing. My plugin adds them as a user to that specific site, but it does nothing to remove/redact/change the default behavior.
A user on one site of your network is essentially a subscriber to all sites on the network. That’s just how Multisite works. They are not, by default, added as an actual user to any site. What my plugin does is auto-add them to the site they signed up through.
My plugin doesn’t isolate anything. You’d probably want something like better network privacy that actually restricts people from other sites on the network. This is unrelated to my plugin at this point.
How do I redirect the users that want to register from checkout page to the per-site custom register site ?
I don’t use WooCommerce. You can ask them how to redirect users to a specific page on checkout. I’m sure they can help 🙂 Then just make that page, per site, the per-site registration page.
Another question is, what is the shortcode for the per-site register form ? I can’t find it. I only see join-my-multisite and join-my-site !
Then you found it, you just didn’t read the FAQ fully 🙂
Read https://wordpress.org/plugins/join-my-multisite/faq/ but this is the part you’re looking for.
How do I use the per-site registration page?
First make a page for your registration. You can name it anything you want, however you can only use top-level pages (so domain.com/pagename/ and not domain.com/parentpage/childpage/). On that page, enter the shortcode [join-my-multisite] around any other content you want.
