What's the Name of That Book??? discussion

The book is fantasy or magical realism.
In the book the child character observes that some letters disappear and objects whose name contain that letter change their properties.
For example, when the letter r disappears objects become softer.
I think the book was by a Spanish speaking author (got it from Cervantes Institute; no they could not help me...). I know that the book was written in Spanish.
The cover had butterflies on it.
I encountered this book about 10 years ago - circa 2009-2012.
Google, Amazon, and other book sites did not help.
This is not a lipogrammatic novel (i.e. a work where certain words or letters are omitted, in the book words are written as usual).
The author is a man.
The child may have had a cold or a flu.

Wild guess:
iSe han comido el alfabeto! by Pierre Gamarra

(There's also a list for that: https://www.goodreads.com/list/show/3... ) :)

A second wild guess...not in Spanish, but maybe you read a translation? Ella Minnow Pea: A Novel in Letters

yakmaia, is this book for adults, teens or kids?

Kris wrote: "yakmaia, is this book for adults, teens or kids?"

I think it was for adults or ”for kids” similar with the Little Prince, i.e. seems for kids but has deeper meaning or can be enjoyed by adults.

What caused letters (only letters?) to disappear? How did the child discover this? How did other people react? Can you give examples of other things that disappeared?

About how long is this book? Are there illustrations inside?