How do you add another language to "text to speech"

Hi, I am just starting. I've made tutorial "talk to me". And I wonder how to add other languages to properties of "text to speech". I would like to add polish language and Polish country. Where can I find simply tutorial how to do this? I would be grateful for simply step by step tutorial.

Welcome Barbara.

Perhaps this will help Backpack/Languages (solved) - #4 by SteveJG

Try these:

add Polish language pl
add Polish country POL