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.
Thanks for posting in the community.
@Cathal_S, appreciate the help.
@sperzednowek, Cathal_S is right. We appreciate users who are keen on sharing their thoughts. We'll take this as feedback as we are always looking for ways to improve our products. I'll consider this thread as complete and will lock the thread after 24 hours.