Hi again,
It does not look like that the “Specjalizacje” is a registered taxonomy. I just tried to access it’s taxonomy terms, but they does not seem to exist, for example: http://mm.emm8.iq.pl/wp-admin/edit-tags.php?taxonomy=specjalizacje&post_type=specjalizacje
Does this “Specjalizacje” taxonomy really exist, or is it just emulated somehow? Because if it does not exist, then it’s not possible to filter by it within the database.