(e.g. if an English specialist teacher has Latin or Mandarin as her secondary subject, those might be added to the curriculum).
Which is a very silly way to build a school's curriculum. What happens if the English teacher leaves or, worse, goes long-term sick? Do you look for an English teacher who can recruit Mandarin? Small pool, to put it mildly. Do you recruit a part-time Mandarin teacher, and if so, out of what budget? Or do you just drop the subject?
One of our local comps played this game, and offered all sorts of languages which sounded terribly impressive. Not a single child, over the course of some years, took one through to GCSE, because to teacher who happened to be able to do a bit of whatever stayed long enough, and the school simply couldn't recruit replacements.
A curriculum means stuff the school commits to offer over a sustained period, such that a child arriving in Y7 stands a reasonable chance of being able to take a GCSE in it. It doesn't means odds and ends of well-intentioned hobby teaching which depends on the presence of particular well-intentioned teachers?