Baby (language)

"Baby" was the name the Eleventh Doctor gave to the language spoken by human babies. It was spoken by infants Melody Pond and Alfie Owens. It appeared to be a one-way language, spoken by babies and heard by the recipients. The listener — in these cases, the Doctor — responded in standard English, which the babies seemed to understand.

The TARDIS translation matrix, however, appeared unable to decipher Baby for other listeners. Only the Doctor appeared able to communicate with them in this way. Judging solely by the Doctor's responses, "Baby" was a complex language with a complete grammar, a large vocabulary, and many rich colloquialisms. (DW: A Good Man Goes to War, Closing Time)

The Fourth Doctor also exhibited an ability to speak Baby. When he and Sarah were in Pescaton-terrorised London, they came across an apparently abandoned baby. Unable to get any information from the child, the Doctor said, "He won't talk." Unaware that the Doctor was likely speaking literally, Sarah then responded, "He can't talk." (AG: Doctor Who and the Pescatons)