postgres@mandreacchio ~ $ pg_upgrade --old-datadir "data.9.0" --new-datadir "data" --old-bindir "/opt/pgsql-9.0/bin/" --new-bindir "/usr/bin/"
Performing Consistency Checks
-----------------------------
Checking current, bin, and data directories                 ok
Checking cluster versions                                   ok
Checking database user is a superuser                       ok
Checking for prepared transactions                          ok
Checking for reg* system oid user data types                ok
Checking for contrib/isn with bigint-passing mismatch       ok
Creating catalog dump                                       ok
Checking for prepared transactions                          ok
Checking for presence of required libraries                 ok

old and new cluster lc_collate values do not match
Failure, exiting