Google only usually adds a countries native language support when they officially sell the device from their online Google store within that country.
As this is a community forum supported by other users and community specialist's then the best way to request that Polish language is added is by leaving feedback for the Google Nest team.
I totally understand that these are good features to use with your Nest Hub, but the Polish language is not available. You can submit feedback about it. Let us know if you have other questions and concerns otherwise, we will be locking this thread after 24 hours.