Good question! I don't know the answer, and I'm sure the dev team will look here occasionally. You may have faster response and a larger audience if you join discord using the link in game, and then go to the #translations channel in discord.

Okay I registered discord channel.
But I am stranger in discord. I don't know how to post message because I have no permission.
I will wait for it.

I think you may need to follow this instruction in order to post?
To gain access to the rest of the server, please react to the first message in #recruitment to gain the Greenhorn role.
When you're ready, join us in #general-discussion , introduce yourself in #your-story , and check out the #faq !

The game's default font does not support Japanese characters, but we have a way to add support for other font sets. It's a bit complicated but basically, we need to pick some fonts to use to replace the core ones - titles, body(UI), comic, and "action."

Once we have the fonts set up, and when we ship that patch, you will be able to choose "use local fonts" in the interface options and your text will show up. This is currently working for Chinese and Russian font sets so it's mainly just about choosing which fonts we want. If you have any font suggestions I'd be happy to hear them.

And yeah discord is usually a quicker way to get answers.

UTF-8 is the correct encoding.

When I see the file in Wildermyth\jre\lib\fontconfig.properties.src,
Japanese font I need are

MS Mincho
MS Gothic

filename.MS_Mincho=MSMINCHO.TTC
filename.MS_PMincho=MSMINCHO.TTC
filename.MS_Gothic=MSGOTHIC.TTC
filename.MS_PGothic=MSGOTHIC.TTC

these fonts are usual in Japan.

Thanks.

I'll take a look at these and see if I can put together a Japanese font placeholder for our next patch, thanks!

this is now available on the unstable beta

I got it. Thanks.
I appreciate your quick support.
You can see a part of result on discord.