In the episode Rebel with out a Teddy Bear, the babies are trying to give Tommy's stuffed lion a bath. Tommy can't reach the soap, so they get the mustard. But how did Chuckie know it was mustard if he can't read? Plus, how did Tommy know that it was soap if HE can’t read either?
I don't read Japanese, but if I was in a kitchen in Japan, I'm fairly certain I'd know the bright yellow squeeze bottle was mustard! They can't read...that doesn't make them stupid! They just know what mustard looks like!