Hi.
I got curious and it seems if you are willing to use lualatex (which
is, I think, currently the most actively developed engine and nowadays
a really good choice), the following solution should work:
--8<---------------cut here---------------start------------->8---
#+TITLE: Doc multi-lingual
#+options: author:nil email:nil toc:nil num:nil date:nil
#+LATEX_COMPILER: lualatex
#+LANGUAGE: jp
#+LaTeX_Header: \usepackage{luatexja}
* Español
Hola
* English
Hi
* French
Ceci c'est en Français
* Japanese
ダウンロード
--8<---------------cut here---------------end--------------->8---
The crucial parts are using lualatex and loading the package
"luatexja". It seems, that the package luatexja is currently one of
the best options to produce Japanese output and it is actively
developed. There is also quite a bit of documentation (see e.g. with
"texdoc luatexja" on the CLI or https://www.ctan.org/pkg/luatexja).
I have no experience with Japanese output and I'm unable to read
Japanese, so I could not judge the correctness or quality. But the
above approach seems to work quite well and it might be possible to
support this solution from the Org side (because only a single package
has to be loaded). The requirements seem to be OK (roughly TeXlive
2020 or newer). The package automatically sets up required fonts (but
it is still possible to override the default font settings) and even
with the default configuration it is possible to use Japanese fonts
inside math mode.
--
Until the next mail...,
Stefan.
