Attached PR 24157 should fix the issue.

> FAIL: test_daemon_threads_fatal_error (test.test_threading.SubinterpThreadingTests)

This test runs code in a subinterpreter which is run in a subprocess. The problem is not in the code run in the subinterpreter, but the creation of sys.stdout in the subprocess.

The test creates a subprocess and redirects its stdout and stderr. In this case, Python doesn't create a _io._WindowsConsoleIO for sys.stdout.buffer.raw, but a regular _io.FileIO object. When the raw I/O is a _WindowsConsoleIO instance, create_stdio() of Python/pylifecycle.c forces the usage of the UTF-8 encoding. But for FileIO, it keeps the locale encoding.

If the locale encoding is "cp932", a CJK multicodec is used. In the main interpreter, it's fine. In a subinterpreter, we hit the bug of the _codecs_jp which doesn't use the new multi-phase initialization API.