A certain use of the parenthetic expression placed between commas, however, has acquired currency in a certain kind of middle grade and young adult book: the kind of book that is sometimes referred to as "multicultural," and is thus placed, so to speak, in its own little virtual parenthetic universe.
In these books, the parenthetic comma phrase or clause is used as shorthand for cultural translation. It pauses the story in order to explain something in a quick aside to the reader, thus demonstrating that:
1. the author expects the reader not to know.
2. the author is assuming that readers who do know won't mind, don't matter, or will never read the book.
3. the author does not trust the reader to understand meaning contextually.
I've seen this little quirk of punctuation used to explain food, customs, clothing, traditions. I've seen it used to translate into English words spoken in foreign languages. I've seen one used in an opening sentence to explain a celebration that is important to the protagonist, even before we've had a chance to get to know the protagonist.
A writer to whom I pointed this out protested that editors want explanation, since books by "us" (i.e., writers of color) are often written for a diverse audience, all of whom may not be familiar with the culture in question. That's true enough, but we have so many rich and wonderful choices. Show the detail through action. Integrate the detail into the story. Make it organic to the story. Return to it after an initial mention and make it clear contextually. Why take the quick and lazy route quite so often? Why not trust the reader?
I'm not against the humble comma, and I'm not suggesting that its use at the beginning and end of a phrase or clause ought to be banned. But when we're writing about food, flowers, festivals, customs, clothing, colloquial expressions in languages other than English, or other elements of culture, that little book-ended aside isn't the only way to offer explanation or translation.