When I use Spanish I do the following, but whatever I do, I try to be consistent:
(1) Integrate it with the rest of the writing and add enough context clues, so the reader isn't lost.
(2) Italicize it and add enough context clues, so the reader doesn't get lost.
(3) Treat is as Spanish and add a footnote to translate it.
(4) Integrate the Spanish, boldly, as is and not differentiate or translate it.
In the beginning of my collection, Not Your Abuelita's Folktales I added some italicized Spanish and something I don't like myself or other writer to do: I added the translation directly after it. In fact, I may get rid of the English in the sample below and add the footnote.
Rita Sifuentes was sitting at her outdated Dell computer while most kids her age were watching YouTube or sleeping in on a Saturday morning. She frowned at it, and her cheek turned up in that funny backwards Y.
"Come on stupid thing! Load faster!" Rita hit the monitor. Her long obsidian black hair was an increasing nuisance that kept getting in her face, even with it tied back. Somehow, strands managed to escape the tightest ponytail. She looked down at her legs. Her long lanky body was a barrio joke in the desert of Nopales, Arizona. The other kids would call her noodle or worse, lumbriz—tapeworm. The kids in her neighborhood were just jealous of her. At least, that's how she reasoned it out because she was going to get out of the barrio, and they were not.
When writers translate Spanish with English right after it, bilingual readers are in essence, reading the same thing twice. It annoys me. I understand why writers do this overwriting, but when long sentences are translated like this, the writing becomes cumbersome.
What I did in most of my collection is add footnotes when necessary or when the whole sentences are in Spanish. In the segment below, I treated the dialogue as you would see it in Spanish, but I did not italicize because speaking in Spanish is normal for the characters.
Her Nana was a bent reed with long bright white hair like the clouds on a hot summer day. Her abuelita would wear it in a long silky braid, and whenever the kids would come outside their fence and make fun of Rita, she would chase after them with her cane, shouting -¡Callensen canijos!- When her parents weren't home she would chuck rocks at them.
 Shut up, jerks!
As a reader, I prefer to see the translation as a footnote, not an end note or glossary. Flipping to the back makes me lose concentration. In fact, most of the time when there is a glossary, I don't even use it.
Footnotes are a great way of keeping true to the Spanish.
The work gets more complicated with ebooks because you will have to create links so the reader can navigate back and forth. This will be a time-consuming part of the book creation I haven't dealt with in the past, but I'm looking forward to it.
In the end what matters is validating other languages and making it easy for all readers to navigate through the usage.
How do you treat other languages in your fiction? Whatever you do, stay true to yourself and the characters.
Keep writing and making thoughtful choices. #barrioblues