The interpreter uses the system ANSI codepage for non-console files. In your case this is codepage 1252. In my current setup I can't reproduce this issue since I'm using the new (beta) support in Windows 10 to configure the ANSI codepage as UTF-8 (65001).

You can force standard I/O to use UTF-8 by setting the environment variable PYTHONIOENCODING. Also, if you want the CompletedProcess stdout decoded as text, in 3.6+ you can pass the parameter `encoding='utf-8'`. For example:

    environ = os.environ.copy()
    environ['PYTHONIOENCODING'] = 'utf-8'
    p = subprocess.run([sys.executable, *args], stdout=subprocess.PIPE, stderr=subprocess.STDOUT, env=environ, encoding='utf-8')
    print(p.stdout)