also str representation of unicode character is different.

This fixes some regressions introduced by nexedi/erp5!1545 when searching the catalog for non ascii text

See merge request nexedi/erp5!1752

Using unicode with a catalog key or related key got broken in the merge
of zope4 support, but using unicode on a translated key (such as
translated_portal_type or translated_validation_state_title) was not
working before.