How to work with multilingual sites using the full site editor and block themes?

you either duplicate your website,
or pay multi-money € ¥ ₪ ¥ $.

The old alternative is to implement multiple languages yourself,
e.g. either a complete duplicate of the website (terrible maintenance)

or a lot of tweaking and customizations (duplicate pages, post types, custom templates per page, where needed, and so forth).

WordPress developers made it clear by now (20 years) that they don’t care about multiple languages, (and some langauges are not even really supported, which is about 1/5 of the world population writing from right to left).

you either pay with money or with (a lot of) time.