the abcs song in japanese goes like a,i,u,e,o,ka,ki,ku,ke,ko and so on so the translator is saying the dragon doesn't know papipupepo as part of the abcs hence cant pronounce the p sounds, since papipupepo is not actually part of the actual song
https://www.youtube.com/shorts/JA7DYU5OXfM
Just for anyone wondering... the last line he sings is referencing the "ten ten" and "maru" letters which one of those lines are the p sound letters. Ten ten (") or maru(°) get added to some of the base letters to create different sounds like pa pi pu pe po.
I hadn't heard that short so thank you. Discovered this song is actually from the opening of an anime and became the alphabet song.
Ryuu's not very good with papipupepo