Lots and lots of non-English speaking patients in the UK - varies on where you work, of course. Sadly, in most cases, languages you learn at school are not the helpful ones. I've found the languages I've most commonly needed have been eastern European and languages spoken in India / Pakistan. I speak fluent French (did A-level and some undergrad study) and used this overseas in a medical setting in French-speaking Africa, but I can count on one hand the number of times it's been useful in the UK.
Entertaining though, to amuse the NICU nurses by having in-depth conversation in French with a parent in French about expressing breastmilk and NG tubes… Niche skills and all that. And I have broken bad news once, in French, in a complex ITU setting. And I once consented a patient for an OGD in Russian. Heh.
Usually, if a language is needed, there may well be a member of staff somewhere who speaks that language who can translate (particularly true for southeast Asian languages), if it's a planned outpatient appointment or something less urgent then interpreters can be booked. Otherwise Language Line is your friend. Language Line is a phone interpreter system where you both sit by a phone (if you're lucky there are two headsets but this has never happened to me) - you tell the interpreter on the other end of the phone what you want to ask the patient, you pass the phone to the patient, the interpreter asks the question and gets the reply etc, then the phone comes back to you and they tell you the answer in English. Desperately tedious and often not that effective, but can nonetheless be a lifesaver at 3am to at least get the basics when the patient doesn't speak a word of English. Otherwise, google translator…
If you're interested in languages and want to learn one, then great, go for it, added bonus if you get to use to at work one day. As has been said (and it's my personal experience too) it can be useful if you want to go overseas in the future to a country that speaks that language. However if you're not that interested really and it's purely to be potentially useful in a UK hospital, then it's probably not worth it.