Hi Francesco,
Yes, that’s certainly possible with the above script. Just make sure you have configured the plugin so that the user can only see the download link in My Account if an invoice was already created. Note that the admin (=shop manager) buttons will still be visible!
I have no explanation for why the invoices are in hungarian, although with WP4.7 it is possible to change the language of the admin per user, and this also changes the language of the invoice. I cannot do anything about this.
If you are considering WPML, I recommend looking at Polylang too. Polylang is much more stable in my experience and also ‘speaks WPML’, which means that most plugins that are WPML compatible are also Polylang compatible.
Good luck!
Ewout