For DE the developers worked with Tribal Consultants.

Apparently, the AOE3DE team has been working closely with Tribal Consultants to have more accurate portrayals of American Indians and First Nations People. I think this is AWESOME! I love any added authenticity to the game. PLUS+ this means we can expect more changes to the Native Civs than we might have previously thought.

https://screenrant.com/age-empires-3-definitive-edition-changes/tldr/6

https://screenrant.com/age-empires-3-definitive-edition-changes/tldr/6