Wild Turkey male and female talking turkey
"We do know that it’s a US term. It’s first recorded in 1824, but is probably much older; one suggestion is that it goes back as far as colonial times. What the explanations have in common is real turkeys.
But the meaning of the phrase seems to have shifted down the years. To start with, it meant to speak agreeably, or to say pleasant things; nowadays it usually refers to speaking frankly, discussing hard facts, or getting down to serious business...
The most prosaic answer is that the “to talk pleasantly” sense came about through the nature of family conversation around the Thanksgiving dinner table. It is also suggested that it arose because the first contacts between Native Americans and settlers often centered on the supply of wild turkeys, to the extent that Indians were said to have inquired whenever they met a colonist, “you come to talk turkey?”
The most complicated explanation is a story about a colonist and a native who went hunting, agreeing to share their spoils equally. At the end of the day, the bag was four crows and four turkeys. The colonist tried to partition the spoils by saying “here’s a crow for you” to the Indian, then keeping a turkey to himself, giving another crow to the Indian, and so on. At this point the Indian very reasonably protested, saying “you talk all turkey for you. Only talk crow for Indian.”
Source: Talk Turkey