After reading the docs more carefully, it's now plain to me that text encoding is not supported yet, so actually it's not a bug :)

However the docs should be improved (and then an assertion could be added too) to prevent people from falling into this trap. Only the `universal_newlines` parameter is explicitly mentioned, while others (including `encoding` and `errors``) are passed to `subprocess.Popen`, which falsely suggests that they should work fine. Moreover, the `std*` properties of the subprocess have a `_transport._pipe.encoding` set to the encoding passed to `asyncio.create_subprocess_*`, but apparently it's not used at all. IMHO this is too messy.

Alternatively this option could be implemented, which would require a new kind of StreamReader and StreamWriter.