You need to ensure your environment supports the UTF-8 format. If you're in Docker, the environment will be set to POSIX. Set the locale to the specified format using the following commands:

$ sudo locale-gen en_US en_US.UTF-8
$ sudo update-locale LC_ALL=en_US.UTF-8 LANG=en_US.UTF-8
$ export LANG=en_US.UTF-8

If all went well you should see the following output:

It should be fine if you're using a different UTF-8 supported locale.