At the very least, the Switch version is launching some time next year.
Dragon Quest Builders 2 was announced earlier this year by Square Enix for PS4 and Nintendo Switch, but only for Japan—a western release date was not actually confirmed. That said, Nintendo may have actually spilled the beans on that in their financial report.
In their report, they have a section for first party releases planned for this year and the next one. First party releases typically refer to games developed in house, as well as any third party games Nintendo will be handling publishing duties for. Apparently that includes Dragon Quest Builders 2, because Nintendo lists it as a first party release for the west in 2019.
This isn’t unprecedented, of course, because Nintendo also handled the Switch conversion of Dragon Quest Builders earlier this year. I have to imagine if the PS4 version is also coming west, Square Enix will be publishing it themselves. But I suppose, at the very least, we know we can expect the game to come out in the west now.