Q. CMOS 7.49. Italics at first occurrence: “If a foreign word becomes familiar through repeated use throughout a work, it need be italicized only on its first occurrence. If it appears only rarely, however, italics may be retained.” What’s your reasoning?
A. I can’t divine the reasoning of the original framers of this advice, but the convention makes sense to me as a reader. When a foreign term is introduced, the italics signal that it isn’t a typo—it’s a word from an unfamiliar language. Once we get the idea—once we learn the word—repeated italics become distracting. If the word occurs only occasionally, however, we might not learn it (especially if there are many foreign terms in the document). In that case, the italics are appropriate for what remains a foreign term.