Harry can no longer speak it
Harry being an accidental Horcrux meant he was bound to Voldemort in so many ways, just like Voldemort was bound to serpents. Not only could Harry speak the language of the snake, but could see through the eyes of Nagini, another of Voldemort's Horcruxes, as it turned out.
There is fan-speculation that the snake Harry released at the zoo in The Philosopher's Stone was in fact Nagini. However, the speculation is false due to the released snake being a male Burmese and Nagini was female and likely came into Voldemort's companionship in Albania.
Nagini, it turns out, was actually a Maledictus—a witch with a blood curse that turns her permanently into a beast (in her case, a giant snake). In the film, the witch is played by Claudia Kim.
In short, no one knows exactly how Nagini ends up as Voldemort's closest ally. Evidently, something happened between the time of her joining Newt and the events of Harry Potter that pushed her to the dark side. She might even have met Voldemort while still human, and he was Tom Riddle.
Nagini is loyal to Voldemort because he can speak with snakes. As a Maledictus, there probably isn't much time after the events in The Crimes of Grindelwald before Nagini falls to her blood curse, becoming a snake forever.
Dumbledore does not use any language to make one think that Nagini is anything more than a snake. But this could be despite his knowledge of Nagini's past because he has to factor his grand plans into everything he tells (or doesn't tell) Harry.
When Harry and Hermione are on the first floor of Bathilda's house, Nagini (inside the corpse of Bathilda) tells Harry to "Come!" from the next room in Parseltongue. In reaction, Hermione jumps and clutches Harry's arm, and the two of them obey the command.
He always seemed like he truly loved Nagini. He must have felt something for Nagini or he wouldn't have given her a part of his soul.
J.K. Rowling recently gave more insight into one of the most controversial characters in the Wizarding World: Nagini, who was known only as Voldemort's snake in "Harry Potter," but appears as a woman in the prequel series, "Fantastic Beasts."
Deathly HallowsEdit
Nagini, Voldemort's snake, then eats Professor Burbage's dead body. A story about her "resignation" from Hogwarts appears in the Prophet, but members of the Order of the Phoenix discount it, as they are unable to locate her anywhere after that.
Albus confirms to Creedence early on in the film that he is in fact a Dumbledore, quashing any rumor that Grindelwald had lied to the young boy in order to sway him to his movement. It is explained that Credence is the illegitimate son of Albus's younger brother, Aberforth (Richard Coyle).
As an unqualified wizard who didn't finish his education, Hagrid was not technically allowed to perform magic.
She was dieting and didn't want greasy food.
Voldemort concludes that he is not yet the true master of the Elder Wand, because Snape killed its previous owner, and thus Voldemort must kill Snape to be the wand's master. Voldemort orders Nagini to kill Snape, and the great snake bites Snape's neck, mortally wounding him.
It wasn't just inanimate objects that could become Horcruxes. Lord Voldemort's beloved snake companion, Nagini, was also transformed into one, and Dumbledore seemed to know it, ominously predicting that a day would come where Voldemort would 'fear for his snake'.
Nagini's Future After The Fantastic Beasts Movies
From that point on, she goes to the forests of Albania, presumably to live out the rest of her life as a gargantuan creature, perpetually bound in her scaly form.
After Voldemort was gone, Nagini decided to follow her dreams. She went to Brazil to join other snakes in the Amazon rain forest. While there, her adventures with Voldemort inspired her to write a song in Parseltongue called "I Thought You Were Pretty Cool But Then You Couldn't Even Defeat a Baby.
Obvious spoiler warning! Yep, that happened: Bellatrix and Voldemort had sex sometime around Order of the Phoenix or Half-Blood Prince, and their wild night in bed led to a child named Delphi Diggory/Riddle/Lestrange. According to Delphi herself, she was born sometime before the Battle of Hogwarts.
The wand will not perform its best for Voldemort until Snape is dead. So saying, Voldemort waves his pet snake, Nagini, in her nest of protective spells, into Snape.
The only "emotion" Voldemort felt when Nagini died was fear because she was the second to last piece of his soul. If Nagini wasn't a horcrux, he wouldn't even have kept her around. When Voldemort said “I regret it” after killing Snape, what was he feeling?
Therefore, when Voldemort used the killing curse against Harry in Deathly Hallows - Part 1, he was actually killing part of his own soul, and Harry was able to survive. And after Neville killed Nagini, all Horcruxes were destroyed.
But now we know Nagini was no simple supervillainous pet, but a human woman cursed with the “Maledictus” blood curse, which, according to Rowling, is a female-only inherited condition which grants the affected individual the ability to transform into an animal at will, until one day, the transformation becomes ...
He finds out for sure immediately after Nagini's attack on Arthur Weasley. This night is significant in many ways. While Harry sleeps, he enters Nagini's mind.
7 horcruxes were diary, ring, locket, cup, tiara, Nagini and Harry. They were destroyed by Harry, Dumbledore, Ron, Hermione, Crabbe, Neville and Voldemort respectively. Amongst them, only Neville and Crabbe didn't know what Horcrux actually were.