To add to the other comments, problems with input methods using Python 3 and Tkinter or IDLE are usually platform-specific issues with the implementation of Tk.  In particular, the issue Jean-Christophe reported with Python 3.1.1 was very likely due to its use of the old Tk 8.4 (at least with the python.org installer).  Current versions of Python 3.2.x for OS X 10.6+ link with the newer Tk 8.5, the very latest releases of which by ActiveState contain important fixes for input methods using composite characters (http://www.python.org/download/mac/tcltk/ has the most up-to-date information).  Also, note to the original poster, you either made a typo in the bug report ("UFT-8" - it should be "UTF-8") or, if you actually tried that locale, it might explain why you had problems.  If someone can reproduce a problem with a current Python 3.2.x or later, please re-open with details.