Absolutely. While you may sometimes have time to look things up, often you won't. I have absent-mindedly arrived overseas without learning "please" and "thank you", and noticed upon fixing that, and using them as appropriate, that everyone was instantly nicer to me, both strangers and the people I was there to interact with. It makes a difference.
I recommend you learn the following things before you go:
- please, thank you, hello, help, yes, no (and the gestures for yes and no too)
- what they say in that country to call people forward from a line (eg "Next!" in many English speaking countries)
- the names of foods you especially like or (more importantly) cannot eat
You should be able to both say and hear these words and react appropriately, which could be as simple as smiling and saying the same thing, or could be getting out your translation device or guidebook and starting the work of communicating.
While you are in the country, you should also know:
- how to say, hear, and read anything that might be your destination - a city name if you're travelling to it, your hotel name, an attraction you want to visit. If you think Tour Eiffel refers to a guided visit, you will be confused or sorry. It is also good to learn east, west, north, and south for extra confirmation that you're getting on the right train or bus
- some numbers. You'll need these for times, prices, bus routes, and so on. If the country writes them differently learn that too.
If you have learned absolutely NO WORDS in the local language, carry props. A map on which you point to where you want to go, some paper from the hotel with their name on it you can show to a cab driver, a printout of your train ticket with your destination on it. "Please help" and pushing your paper at someone will probably work. Getting your phone to say "which is the platform for the airport train?" might, but then again it might not.
Imagine yourself at the mall and a stranger comes up to you. They hold their phone out to you and want you to read it, or they push a button and their phone says something ungrammatical in a robot voice. Would you help those people? Would it make a difference if the conversation started "Hello, can you please help me? I am lost." and then the phone-offering or paper-showing started? I think it would. Knowing just a dozen local words will make an enormous difference and it is not hard to do.
One other thing: if you can convincingly say "no thankyou" in a bored voice in the local language you will be pestered far less by the tchotke-sellers and would-be pickpockets or whatever that seem to hang around most tourist attractions. I learned this by accident in France. I was being polite declining in their own language and the one time I slipped and used English I got a frighteningly hard sell and a lot of pressure and aggravation. That never happened with the bored French.