Multilingual network on subdomains

Hello,

I would create something like:

Network:
https://kuzniczysko.pl/
https://fundacja.kuzniczysko.pl/
https://mlyn.kuzniczysko.pl/

And multilingual for some of them (I prefer the multisite way the most):
https://mlyn.kuzniczysko.pl/de/
https://mlyn.kuzniczysko.pl/en/

By Network I mean that I could “duplicate” post for example for both https://kuzniczysko.pl/ and https://fundacja.kuzniczysko.pl/ – use the same media resources and canonical url (I have somewhere plugins for that).

By multilingual I mean that I could use plugin like Multisite Language Switcher for translating posts (generally I have gallery post type and only some of them will be on sublanguages)

As I figured the one way is to use WP Multi Network with WP Multisite (+ Multisite Language Switcher) on each subdomain. However I think I am wrong – I can’t set WP Multisite on https://mlyn.kuzniczysko.pl/ (by the way there are no selection of subdomain/subfolders on activating WP Multisite from Tools menu), because I get 500 Internal Server Error and any known fix, mainly for .htaccess, doesn’t take an effect here.

Is there any way I can do it? My client would have such big network (there will be much more multilingual subdomains), but if it’s not possible there are an alternative – normal WP Multisite Network and multilinguage did on custom post type (as was before), but I don’t like this way – it’s more dirty functions.php‘s code and this is no so clean for SEO (especially lang metatags). I would multilingual were so clean as my standalone simple script – https://maciej.kuzniczysko.pl/tools/rom/pl/ (subdomain doesn’t related to network).

Many thanks for any help,
Greetings!