Songs he sings
By “sings”, I mostly mean “hums”, except for “Ee ai ee ai oh” (from “Old McDonalds”), which he articulates quite well.
For the other tunes, there is often a hint of a shadow of words, which is why I know (or guess) that it’s in one particular language, even if there are songs with the same tune in different languages. The (language-specific) song he hums is listed first, followed by, in parenthesis, songs with the same tune in other languages that he is exposed to.