Proof of concept of patch fixing this issue:
 - parse_syntax_error() reads the text line into a PyUnicodeObject* 
instead of a "const char**"
 - create utf8_to_unicode_offset(): convert byte offset to a number of 
characters. The Python version should be something like:

   def utf8_to_unicode_offset(text, byte_offset):
      utf8 = text.encode("utf-8")
      utf8 = utf8[:byte_offset]
      text = str(utf8, "utf-8")
      return len(text)

 - reuse adjust_offset() from 
py3k_adjust_cursor_at_syntax_error_v2.patch, but force the use of 
wcswidth() because HAVE_WCSWIDTH is not defined by configure
 - print_error_text() works on unicode characters and not on bytes!

The patch should be refactorized:
 - move adjust_offset(), utf8_to_unicode_offset(), utf8_len() in 
unicodeobject.c. You might create a new method "width()" for the 
unicode type. This method can be used to fix center(), ljust() and 
rjust() unicode methods (see issue #3446).