I've run a few tests for you. I mean that as a comment but it doesn't fit into a comment so I must send it as an answer.
In [1]: import locale
...: import functools
...:
...: locale.setlocale(locale.LC_ALL, 'fr_FR')
...: test=('pêche','pomme')
...: sorted(test,key=functools.cmp_to_key(locale.strcoll))
Out[1]: ['pêche', 'pomme']
In [2]: import locale
...: import functools
...:
...: locale.setlocale(locale.LC_ALL, 'fr_FR.utf8')
...: test=('pêche','pomme')
...: sorted(test,key=functools.cmp_to_key(locale.strcoll))
Out[2]: ['pêche', 'pomme']
In [3]: import locale
...: import functools
...:
...: locale.setlocale(locale.LC_ALL, 'fr_FR.ISO-8859-1')
...: test=('pêche','pomme')
...: sorted(test,key=functools.cmp_to_key(locale.strcoll))
Out[3]: ['pêche', 'pomme']
In [4]: import locale
...: import functools
...:
...: locale.setlocale(locale.LC_ALL, 'en_GB.ISO-8859-1')
...: test=('pêche','pomme')
...: sorted(test,key=functools.cmp_to_key(locale.strcoll))
Out[4]: ['pêche', 'pomme']
Until now I could not get a result with returning 'pomme, pêche' instead of 'pêche, pomme'. I always get it in the order as you would like.