The mildly uncomfortable aspect of it is that <i lang="la">veni, vidi, vici</i> might change the font the text is rendered in, because the generic font families (e.g. serif, sans-serif, cursive, monospace) can vary by language. For me, for example, my usual serif is Equity A, but in Latin it changes to Noto Serif and I haven’t been bothered to patch this up in my Firefox config because it takes far too much effort, requiring changes in a number of languages (not such as French (fr), but yes such as Latin (la) and Māori (mi)). Or sans-serif: Concourse 4 becomes Noto Serif. This will honestly cause me to omit lang=la in some iffy cases where I would write lang=fr on a similar word or expression from French.