Ubuntu Linux 18.04 LTS。
$ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 18.04.3 LTS Release: 18.04 Codename: bionic
The event that was happening is the same as TL; DR. I was in trouble because I couldn't switch to Japanese input.
IME uses Mozc.
After a little research, I found the following article, so I switched Java used to start IntelliJ and tried it.
Click here for Java bundled with IntelliJ (used for startup by default).
jbr/bin/java --version openjdk 11.0.5 2019-10-15 OpenJDK Runtime Environment (build 11.0.5+10-b520.17) OpenJDK 64-Bit Server VM (build 11.0.5+10-b520.17, mixed mode)
Look at the following document and select the method to set with environment variables this time.
Changed to start with OpenJDK 8.
This time, this is the solution.