On my mission in Guatemala, we didn’t use the King James version of the bible. Instead, we used a popular Protestant translation called the Reyna Valera. This raises all sorts of fun questions.
For example, the Book of Mormon in Spanish doesn’t use the Reyna Valera language for its quotes from Isaiah, Matthew, Malachi, and so on. It uses King James English, translated into Spanish by the church translators.
That creates questions about how Spanish members should approach Biblical texts like Isaiah which are also reproduced in the Book of Mormon. Where the Book of Mormon (translated KJV) differs from the Reyna Valera language, should they view the Book of Mormon language as superior? In places where it exactly duplicates the KJV text, is there something specific about the particular language of the Book of Mormon? Or is it simply adopting a popular Biblical text? (In which case, there may not be any reason to favor one popular text (KJV) over another (Reyna Valera)).
Also, how does a Spanish-speaking member accurately look at things like the subtle changes between KJV Isaiah and BoM Isaiah? A good gospel doctrine teacher can point out little changes in language and content and what they might mean (like the “ships of Tarshish” verse). LDS scholars like John Tvedtnes have written lengthy papers on the Isaiah variants in the Book of Mormon, and what we can learn from the ways that BoM Isaiah differs from KJV Isaiah. (See, e.g., this paper.) That kind of analysis doesn’t make sense in the Spanish-speaking context. There are all sorts of differences between BoM Isaiah and Reyna Valera Isaiah, and I’m sure that most of them come from the differences in underlying translations. With only a Libro de Mormon and a Reyna Valera — the tools available to an average Spanish-speaking member — there is really no way to do a Tvedtnes kind of analysis and see where Joseph Smith’s variations are.
The same kinds of limitations apply to conference talks. When a speaker cites a Bible verse, do our translators simply translate KJV language? But then the Spanish-speaking member looks it up, and it looks like President Hinckley is misquoting Isaiah. Or, do we substitute in Reyna Valera language? What if the two readings differ in some significant way (due to differences in the underlying translations)?
These questions could be addressed by using a Spanish-translated KJV. But that possibility highlights some of the other considerations. For example, there are interesting questions about the missionary use of adopting local customs. I saw more than one member vigorously attack the Testigos — Jay Dubs — because they had their own Bible, their own translation, which was just not the same as the good old Reyna Valera. Some members memorized passages where the Jehovah’s Witness translation was significantly different from the Reyna Valera, for the sole purpose of Bible-bashing.
And finally, it strikes me that translating the KJV into Spanish might cast a spotlight on the KJV’s own problems. It was a widely accepted standard in Joseph Smith’s day. Today, there is extensive scholarship on the numerous problems of the KJV — bad texts used in the translation, wholly fabricated insertions (Johannine Comma, anyone?), and so on. A century and a half ago, Joseph Smith spoke in relatively vague terms about problems in translation. Today, scholars know (or strongly suspect) the locations of many specific problems in the KJV. Any project of translating the KJV would bring up all sorts of questions about the propriety of continuing to use the KJV today — probably not something the church really wants to get involved in.