The cause of #12213 is in dump_stdout and dump_stderr:

      print(read_no_crs(<filename>))

Commit 6f6f5154 changed read_no_crs to
return a unicode string. Printing a unicode strings works fine as long
as sys.stdout.encoding is 'UTF-8'.

There are two reasons why sys.stdout.encoding might not be 'UTF-8'.

* When output is going to a file, sys.stdout and sys.stdout do not respect
  the locale:

  $ LC_ALL=en_US.utf8 python -c 'import sys; print(sys.stderr.encoding)'
  UTF-8
  $ LC_ALL=en_US.utf8 python -c 'import sys; print(sys.stderr.encoding)' 2>/dev/null
  None

* When output is going to the terminal, explicitly reopening sys.stdout has
  the side-effect of changing sys.stdout.encoding from 'UTF-8' to 'None'.

      sys.stdout = os.fdopen(sys.__stdout__.fileno(), "w", 0)

  We currently do this to set a buffersize of 0 (the actual
  buffersize used is irrelevant for the sys.stdout.encoding problem).

Solution: fix dump_stdout and dump_stderr to not use read_no_crs.