'Thank you' and 'Excuse me'
I’m off to Finland in about a week for a couple armonica concerts. There’s no way I can learn enough Finnish to be useful. Meanwhile, concerts like this are invariably in larger cities with plenty of English speakers so that’s not really a problem.
Nevertheless I have learned, wherever I go, that it is really helpful to learn at least two words in the native language:
“Thank you“ — when they get the waiter/waitress in the restaurant who speaks a little English, and we get through ordering lunch, it seems gracious to me to be able to say ‘thank you’ in their native language,
“Excuse me“ — for when I bump into someone on the subway, etc.
There are other good words, of course, like 'please'. But usually you follow 'please' with a sentence: "Please can you tell me how to get to the post office." So 'please' by itself doesn't do you much good unless you can actually speak the language a little. And 'hello' is good too, except that usually it is the opening of a conversation—that you won't be able to manage in their native language without some real facility.
Of course if you are actually going to learn to speak the language, 'hello' and 'please' will be near the top of your vocabulary list.
But if you can only learn a couple words, 'Thank you' and 'excuse me' will get you through a lot. Wait, just those two words will get you through a lot of Life in general!