On regards of some readers’ frustrations for the Spanish parts in the book, I don’t think the question (or complaint) is “Who’s to say that his audience is primarily Spanish?” Perhaps the question should be Why do we have to limit ourselves to English only?
Contrary to what happens in other countries, there is no official language in the US. In other words, nowhere it is written that the communication should be only in English. The latter is clearly a good choice if we consider English as the global language. Hence, for practical purposes, it makes sense to be the most used. However, the fact that it is the most convenient, doesn’t mean it should be the only one spoken. Take Switzerland, fort instance. It is separated into three main regions, each one of them with a predominant language: Italian, French, and German. The answer Swiss people found was to teach and learn three languages in school (actually 4 if we consider English).
I believe that if we want to understand multiculturalism, we need to speak more than one language. Each particular language has its roots in different frames of mind, different ways of thinking, different perspectives. The more languages a person knows the wider the spectrum to deal with humans points of view, perceptions, and realities.
In my personal experience, I can say that reading a story in Spanish or in English brings two different worlds to my mind. Risking to sound simplistic, I believe English has tremendous power for narrative and non-fiction. It is precise and can create words easily by combining terms. Spanish, on the other hand, tends to be so flourished that speaking in metaphors is the most natural thing. There are dozens of verb tenses to indicate the slightest nuances in time… My point is that each language is a world in itself and speaks volumes of the people using it for expression.
Multiculturalism is not a matter of reading about other cultures, it is a process of understanding and perceiving as ”the other”. For that matter, we shouldn’t limit ourselves to only one language. I don’t mean, of course, that we have to learn the thousands of languages and dialects that exist in the world, but at least something more than English if we really want to consider ourselves citizens of the world.