Add PyUnicode_DecodeLocaleAndSize() and PyUnicode_DecodeLocale()

* PyUnicode_DecodeLocaleAndSize() and PyUnicode_DecodeLocale() decode a string
   from the current locale encoding
 * _Py_char2wchar() writes an "error code" in the size argument to indicate
   if the function failed because of memory allocation failure or because of a
   decoding error. The function doesn't write the error message directly to
   stderr.
 * Fix time.strftime() (if wcsftime() is missing): decode strftime() result
   from the current locale encoding, not from the filesystem encoding.

Doc/c-api/unicode.rst

@@ -699,6 +699,39 @@ Extension modules can continue using them, as they will not be removed in Python
    throughout the interpreter whenever coercion to Unicode is needed.
 
 
+Locale Encoding
+"""""""""""""""
+
+The current locale encoding can be used to decode text from the operating
+system.
+
+.. c:function:: PyObject* PyUnicode_DecodeLocaleAndSize(const char *str, Py_ssize_t len, int surrogateescape)
+
+   Decode a string from the current locale encoding. The decoder is strict if
+   *surrogateescape* is equal to zero, otherwise it uses the
+   ``'surrogateescape'`` error handler (:pep:`383`) to escape undecodable
+   bytes. If a byte sequence can be decoded as a surrogate character and
+   *surrogateescape* is not equal to zero, the byte sequence is escaped using
+   the ``'surrogateescape'`` error handler instead of being decoded.  *str*
+   must end with a null character but cannot contain embedded null character.
+
+   .. seealso::
+
+      Use :c:func:`PyUnicode_DecodeFSDefaultAndSize` to decode a string from
+      :c:data:`Py_FileSystemDefaultEncoding` (the locale encoding read at
+      Python startup).
+
+   .. versionadded:: 3.3
+
+
+.. c:function:: PyObject* PyUnicode_DecodeLocale(const char *str, int surrogateescape)
+
+   Similar to :c:func:`PyUnicode_DecodeLocaleAndSize`, but compute the string
+   length using :c:func:`strlen`.
+
+   .. versionadded:: 3.3
+
+
 File System Encoding
 """"""""""""""""""""
 
@@ -739,6 +772,13 @@ used, passing :c:func:`PyUnicode_FSDecoder` as the conversion function:
    If :c:data:`Py_FileSystemDefaultEncoding` is not set, fall back to the
    locale encoding.
 
+   .. seealso::
+
+      :c:data:`Py_FileSystemDefaultEncoding` is initialized at startup from the
+      locale encoding and cannot be modified later. If you need to decode a
+      string from the current locale encoding, use
+      :c:func:`PyUnicode_DecodeLocaleAndSize`.
+
    .. versionchanged:: 3.2
       Use ``'strict'`` error handler on Windows.