Groot speaks a language all his own that few understand, but in Avengers: Infinity War, Thor revealed that he was one of them. The reason he knows the language, however, is different from what he states in the film, according to filmmaker James Gunn."Thor was making a joke, as he is prone to do, when he said Groot was an elective [on Asgard]," the Guardians of the Galaxy director said when asked about the matter on Twitter. "Being a god of sorts he doesn’t have the same high bar for understanding Groot as the Guardians do."
In a related tweet, Gunn was asked why Peter Quill couldn't understand the language, despite wearing a universal translator. "He doesn’t have a universal translator," Gunn said. "He has a translator. And it doesn’t have all languages in it (it didn’t have Sakaaran in the first film for example). And people don’t learn Groot through knowing the language - they learn it through connecting with Groot."
It can be inferred that Thor's god-like status must give him a linguistic advantage then, as he proficiently understood Groot's language shortly after first meeting him, while most of Groot's teammates remain incapable of comprehending him without assistance.
In fact, outside of Thor and Groot's frequent companion Rocket, few if any have been shown capable of understanding the alien's tongue, which consists only of the phrase "I am Groot."
Written and directed by James Gunn, Guardians of the Galaxy Vol. 3 is set to begin filming in February 2021. Its current release date is targeted for 2023.
Source:Â Twitter
NOTE: This story was updated Dec. 29 with updated information.