Some parts will be in Italian/French like the movie. But not to worry, anything in another language other than english will be dialogue that is either unimportant to the story arc, simple to understand, or conveyed in english.
Some chapters will be in Elio's perspective like the novel and movie.
Some chapters will be in Oliver's perspective.
The foundation of this sequel is derived from what Luca has confirmed in interviews about the sequel. Ex: 7 years later, Elio is 24 and Oliver is 31, The aids epidemic will be addressed, Once More will be the opening scene, etc.
Other things will be altered by my personal preference on how I'd like oliver and elio to end up.
That's everything! Enjoy!