alembic/sqlalchemy fails to migrate when PostgreSQL lc_messages is set to 'non-ascii' language

When you try to upgrade from juno to kilo and your database server is PostgreSQL configured with for ex. `lc_messages = 'pl_PL.UTF-8'`, alembic migration will fail with following mysterious traceback:

  File "/usr/lib/python2.7/dist-packages/neutron/db/migration/alembic_migrations/versions/589f9237ca0e_cisco_n1kv_ml2_driver_tables.py", line 113, in upgrade
    sa.PrimaryKeyConstraint('tenant_id', 'profile_id')
[......]
  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/default.py", line 436, in do_execute
    cursor.execute(statement, parameters)
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc5 in position 20: ordinal not in range(128)
dpkg: error processing package neutron-common (--configure):
 subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of neutron-server:
 neutron-server depends on neutron-common (= 2015.1.0-1); however:
  Package neutron-common is not configured yet.

when instead it should report this:

  File "/usr/lib/python2.7/dist-packages/sqlalchemy/engine/default.py", line 439, in do_execute
    cursor.execute(statement, parameters)
oslo_db.exception.DBError: (ProgrammingError) type "profile_type" already exists
 "CREATE TYPE profile_type AS ENUM ('network', 'policy')" {}

This exception is thrown due to localized error message: `BŁĄD: typ "profile_type" już istnieje` which contains non-ascii characters. I guess there should be no constraint on server response string (error) to be an ascii string.