I wrote thousands of diplomatic cables during 21 years in the U.S. Foreign Service, and I dread calculating how many I’ve read. Here is an insider’s view of how to read them.

Don’t believe everything they say (and don’t say). A good diplomat will of course report what foreigners say as accurately as possible, but even when she does there are still several sources of uncertainty. Most important is language.

I have top scores in both Portuguese and Italian, but I did not always understand every word an interlocutor (that’s diplomatese for “person,” implicitly someone worth talking to) said to me i...