i doubt they want to conquer the japanese market, it's probably more about convincing japanese devs to release their games on the XBox instead of only doing ps4/switch.
This is exactly the reason, and he's talked about it before. Spencer has outright stated he knows they have little to no chance of actually getting the Xbox console to make a dent in the Japanese market anytime soon, for a multitude of kinda baked-in reasons. However, what he does want, is to ensure more major Japanese-developed titles actually see Xbox releases at all, and preferably day-and-date with other platforms - not a year or two later. He specifically mentioned Nier Automata in the interview in 2018 where he made these comments. Nioh would be another good example.
He also mentioned services like Game Pass as potentially helping with this effort, as he can reach out to smaller Japanese game devs and say something like "okay, maybe your game doesn't have enough of a worldwide market to do a proper "release" - but perhaps we can add it to Game Pass instead?"
We've also seen the fruits of some of these effots, with Kingdom Hearts and Final Fantasy libraries finally coming to the Xbox, not to mention his efforts on something like Phantasy Star Online 2 - which I'd guess is literally only happening after 8 years, because Spencer/Xbox probably offered to fund the localization and North American hosting (there's a conspicuous Azure logo at the end of the E3 2019 trailer).