Multilingual is a must-have feature for a CMS. And I think it's more a WordPress's problem than Gutenberg's.

As there are more than a year before the Phase 4 starts, I think it's a good time for other multilingual plugins to collaborate with WordPress core team to contribute or suggest the best way to do this. Plugins such as WPML, MultilingualPress, Polylang have been on the market for years, maybe a decade, so they understand the problem in and out. And their help is really valuable (of course only when they're willing to).