Is it the author's job to provide translations? If the author's experience of life is a mix of English and Spanish then that is a valid voice; so the reader's struggle might actually give them a better understanding that their English isn't the only way English speakers communicate - as opposed to translation notes, which would imply the Spanish wasn't an equally valid part of the language as spoken. I wonder whether the same critic would challenge Latin epigrams if there were no translations?
Is a realistic life that is more hectic than the reader's unrealistic? If the author's experience is like a soap opera, then relegating it to clearly made up privileges a particular low-drama lifestyle.
I am not sure how society will evolve, but I could easily see language becoming more of a mix of languages, so saying people who portray a world that isn't restrained people speaking English aren't quite as proper novelists does risk putting all speculative fiction, and diverse speculative fiction especially, towards the fringes.