life in a bilingual household, or why don't they teach the word "wrinkle" or "wrinkly" in Spanish textbooks

The scene: our bedroom
The action: Elias begins to stuff his tie in his jacket pocket

Me: (in English): Don't do that, your tie is going to get wrinkled!
E: What?
Me: If you put your tie in your pocket it's going to get wrinkly.
E: What is wrinkly?
Me: Wrinkled
E: I don't know what is?
Me: (in Spanish) I don't know the word in Spanish, it's what happens when you need to iron something.
E: Oh, yes. Arrugado.
Me: Fine, arrugado. Wrinkly. You should learn that word, wrinkly. It's important.
E: Ok.