We know that Tarzan speaks Mangani, the language of the great apes, but he is supposedly also able to understand other species, and even converse with some.
In the first Tarzan book, “Tarzan of the Apes” (1912) Tarzan made friends with, and was able to ride, Tantor the elephant. We are not told how, but I presume that Tarzan was able to speak to the elephant in a way that the elephant would understand, i.e. in elephant language. (p. 62)
Tarzan writes (since he cannot then speak English) to D’Arnot that he speaks only the language of the apes, and a little Tantor, the elephant, and Numa, the lion, but understands the other folks (animals) of the jungle (p. 162).
By the end of the first book, Tarzan speak French, and English (with a French accent), having learned from D’Arnot.
By the end of the second book, “The Return of Tarzan” (1913), Tarzan spoke French, English, Arabic, and Waziri (p. 160). The Tarzan books referred to here are these ones.
In “Tarzan the Terrible” (1921), he also is known to speak and read fluent German.
In the other books, Tarzan is also fluent in several languages, including Mangani. Never is he the “me Tarzan you Jane,” of Johhny Weismuller Tarzan movie fame. While most of the movie versions make him out to be some linguistic imbecile, the actual books of Edgar Rice Burroughs show him to be a quick language learner, and eventually fluently speaking the language of those with whom he converses.