On Glossaries and Italicizing

Author and creative writing teacher John Gardner contends that "the most important single notion in the theory of fiction" is that of fiction or storytelling as a "vivid and continuous dream" (The Art of Fiction, 97). The vivid part is easy to figure out: make an image of your story for the reader. Throw in details where details are necessary; for for the concrete, the tangible. That movie in a reader's head, right?
As to the "continuity principle" of Gardner's theory, this is a bit messier. He states that "the reader should never be distracted from the image or scene," presumably a vivid image or scene (98). Implied in this statement is that whatever would distract the reader is the result of something the writer did or didn't do or did poorly. "[T]he sensitive reader shrinks away a little, as we do when an interesting conversationalist picks his nose" (99). Get the picture?
So, a good story should be able to carry itself because it is a good story. But what if the writer of that good story uses Spanish? At a reading for my first novel, The Jumping Tree (2001) I was asked by a girl named Rachel why I wouldn't use a glossary of Spanish terms like Gary Soto does in his work. I debated wether to tell her the truth, academic though the answer might be, or to give her some stock answer. I went with the truth: that back in my day reading Shakespeare in high school, if I didn't know the meaning of a word, the teacher would recommend I crack open a dictionary and find out for myself. Shakespeare didn't provide readers with a glossary of his English. I added that I did include context clues as to the meaning of words and phrases, so a reader shouldn't find herself completely lost.
But actually did give it some thought during the writing of the book: a glossary at the bottom of the corresponding page or at the end of the book, or not at all? I went with the last choice--none at all. And mostly because when I am in the middle of a good story and the author uses a language foreign to me the last thing I want to do is to interrupt the flow of the story, the continuity of it by turning to the end of the book, finding out what a word might mean, then try to get back into the groove of the story where I left off. I can well find the very spot where I dropped away, but it's unlikely that I get back into the emotional groove. If a word or phrase knocks my reader away out of the flow, then shame on me, but normally I try to think through my use of Spanish: is is necessary, is it authentic in use, is it smooth?
I don't italicize either, mostly. I grew up in the U.S. speaking both Spanish and English, and so by default both are U.S. languages. Neither foreign to me, a U.S.-born citizen, as the user of them. I will use italics when in a conversation a character who is not a U.S. citizen speaks his or her language and it is a foreign language to the narrator. So if Rey's Mexican grandmother in The Jumping Tree speaks Spanish, in that case I would italicize. When Rey speaks Spanish to his best friend, Chuy, both of whom are U.S. citizen, then no italics. It's that simple. Or that complicated. Take your pick.