i think i can answer your question in italian
"turn into"=diventare un'altra cosa o entrare nel una cosa invece di sul una cosa, per esempio una foresta
turn into =to become something else or to enter into something instead of on something, for example a forest.
ex: "After they had been walking down the road for a few miles, the hikers decided to take a break by turning into the forest for their lunch."
or "After you reach the street, turn into the parking lot for the restaurant"
"turn onto" si usa spesso per un cambiamento delle strade
"turn onto" is used often for a change in streets
ex: from highway 40, you turn onto Rose Boulevard
Please correct any italian mistakes I may have made.