There are lots of books about sibling rivalry but this one, by contrast, is about two sisters who get along well together and enjoy sharing experiences. Since the girls in the book are twins, it would be an especially appropriate gift for real-life twins.
The words aspect of the book is that it is written in three languages, English, French and Spanish. I enjoyed trying to figure out the meaning of the individual words and phrases in the languages I don't know and some kids will probably like doing that, too. Although I took French in school decades ago and never studied Spanish I found that I could understand more of the Spanish words than the French ones.
My Sister is My Best Friend would be a great help to kids who know one of the three languages and are trying to learn another and already bi- or multi-lingual kids will like it.
Of course children who can only read or hear the story read in one language will enjoy it for the cheerful experiences the sisters share. The cute illustrations by Clara Batton Smith add to the pleasure of the book.