PEP 540: Fix effects of the PEP 538

pep-0540.txt

@@ -144,9 +144,15 @@ The POSIX locale enables the locale coercion (PEP 538) and the UTF-8
 mode (PEP 540). When the locale coercion is enabled, enabling the UTF-8
 mode has no (additional) effect.
 
-Locale coercion only impacts non-Python code like C libraries, whereas
-the Python UTF-8 Mode only impacts Python code: the two PEPs are
-complementary.
+The UTF-8 has the same effect than locale coercion:
+``sys.getfilesystemencoding()`` returns ``'UTF-8'``,
+``locale.getpreferredencoding()`` returns ``UTF-8``, ``sys.stdin`` and
+``sys.stdout`` error handler set to ``surrogateescape``. These changes
+only affect Python code. But the locale coercion has addiditonal
+effects: the ``LC_CTYPE`` environment variable and the ``LC_CTYPE``
+locale are set to a UTF-8 locale like ``C.UTF-8``. The side effect is
+that non-Python code is also impacted by the locale coercion. The two
+PEPs are complementary.
 
 On platforms where locale coercion is not supported like Centos 7, the
 POSIX locale only enables the UTF-8 Mode. In this case, Python code uses