Haha, it's a bit of a pun. Mary Poppins is a character from the book and movie series with magical powers, so "Mary Poppin's Language" could refer to her ability to speak different languages fluently or even have magical language abilities (like being able to understand animals). But in this case, it just means I don't know what you're talking about.

Joke worked so much better in my head.

I promise i am quick on my feet normally

Lets pretend this never happed. 😂😓