On our recent holiday to Barcelona, Jess and I got to pondering one of those questions that people like us sometimes like to ponder: what is the most useful phrase to learn how to say in a foreign language?
All this started because we began by discussing the "uselessness" of the phrase "do you speak English?" (or it's equivalent, in whatever language). This phrase is functionally completely useless, because the answer is only useful if it is yes. You don't lose anything in pure communication terms by asking "Do you speak English?" in English, rather than, say, "Hablas Ingles?". There are social reasons why "Hablas Ingles?" is not actually completely useless - people are likely to be better disposed to you if you bothered to learn how to ask even such a basic question in their own language, but for the purposes of this discussion, let's assume that people are all Vulcans, and that language is only used to convey information, rather than having any cultural or social function.
What phrase might be useful to know in Vulcania (not sure why I just invented a place where Vulcans live, instead of going with the more usual Planet Vulcan)? You could know how to ask directions to the bank, but there are hand gestures, and various other ways you could manage to get that information across. If we're talking about somewhere on Earth, then the chances are that you'll be able to find someone that knows the English word for "hospital" or "taxi". Actually, the word for "hospital" is likely to be irrelevant - if you desperately need a hospital for some reason, you're probably bleeding or screaming out in pain, or otherwise going to be able to indicate what the issue is. The only thing I managed to come up with that might be useful is if you have some specific medical condition - might be good to know the word for insulin if you're diabetic, or for peanuts if you have a severe allergy. Other than that, I'm stuck trying to think of the one phrase I'd absolutely need to know.
On a related note, the phrases I actually do know how to say in more than three languages are "I love you" (totally useless, I'd have thought), "kiss me" (not quite as useless, but again, non-verbal communication might work better for that), "f*ck off" (again, can usually be expressed non-verbally) and how to count to 10 (pretty much totally useless, given that I have 10 fingers on each hand). Wonder what I'd learn next.