In short, I do not understand how this passes on Linux.

This is python3-3.4.6 on sles12:

>>> 'h\xe9\u20ac'.encode('utf-8')
b'h\xc3\xa9\xe2\x82\xac'
>>> ascii('h\xe9\u20ac'.encode('utf-8'))
"b'h\\xc3\\xa9\\xe2\\x82\\xac'"
>>> 'h\xe9\u20ac'.encode('utf-8').decode('us-ascii', 'surrogateescape')
'h\udcc3\udca9\udce2\udc82\udcac'
>>>

This is python3-3.7.0 on AIX:
>>> 'h\xe9\u20ac'.encode('utf-8')
b'h\xc3\xa9\xe2\x82\xac'
>>> ascii('h\xe9\u20ac'.encode('utf-8'))
"b'h\\xc3\\xa9\\xe2\\x82\\xac'"
>>> 'h\xe9\u20ac'.encode('utf-8').decode('us-ascii', 'surrogateescape')
'h\udcc3\udca9\udce2\udc82\udcac'

If I am missing something essential here - please be blunt!