So I can do nothing to do for adding Japanese support to this game?

Let me explain current situation of pc gaming scene in Japan:

Back to late 90' there is only a few games have Japanese language so we have to learn English to play best games in the world, so I did. 

Nowadays, situation was improved greatly. About half of AAA games support Japanese at launch, and many most illuminated indie games have that too, thanks to Switch's popularity. People can play those games easily, without language problems. On the other hand, game without Japanese support are almost the same that doesn't exist. Even had over 85 metascore, even had 50k concurrent players in steam, almost no one know them.

"Well, we have plenty of good games that can be playable without language difficulty, why do we need to pick games without native language support?"

It's sad, but understandable.

That's reason why I made fan-translation for some (mainly strategy) my favorite games, including Surviving Mars, Unity of Command 2, Panzer Corps 2, Against the Storm, Warhammer 40K: Chaos Gate - Deamonhunters(my latest work). Sadly it might be too late to humankind to become popular in Japan. But please consider to those 2 options below:

1. Add official language support

It's best scenario for me, but it may cost too much, no guarantee to commercial success.

2. Make localization to be moddable

You have Japanese translation mod in almost no time. (depends how difficult to import texts into mod)

Additionally, it makes happier not only me, people live in other countries that have not official language support atm.

I hope Amplitude games (not only Humankind) have attention in my country someday.