is it true that if a person is encouraged to do something unconscioulsy, the will automatically continue doing it. For example: if a person is listing many word, and whenever a person says a plural word, and the other person smiles or nods their head every time, will the person automatically start saying more plural word without actually knowing it themselves?is that true?

I'm not familiar with your example, but yes it will work. This is an example of positive reinforcement. Quite common training technique for (most commonly, that I know of) dogs and even babies.