In Scandinavia and the Netherlands, nearly everyone speaks English remarkably well. (In Scandinavia, speaking two foreign languages is totally normal. They start English in first grade and a second language in fifth grade. I've heard that Dutch schools require three languages, usually English, French, and German.) Just say "Excuse me," or "Hello" before you start talking, to give them a chance to make the mental adjustment.
In other countries, just learn how to say, "Do you speak English?" in the local language. If the person you are talking to doesn't speak English, they can almost always find someone who does.
For emergencies, get a Berlitz pocket phrasebook for each country. If you don't want to venture pronouncing a foreign language, just point. The advantage of the Berlitz books is that they have a list of possible answers that the local person can point to.
One thing you may not have considered about apps: Using your phone's cellular data in a foreign country costs two arms and two legs, and even if you have a plan that supposedly includes foreign data, it may be limited to 2G. When I travel overseas, I turn the cellular data off and just use my hotel's wi-fi or any other wi-fi I can find.
But don't worry too much about language, even in countries where no one speaks English.
My family took an extended trip to Europe in the late 1960s. One night, we arrived in a Danish town where all the hotels were full, but there was a kiosk at the train station where you could find rooms in a B&B. We ended up in an old house full of antiques run by an old lady with a little dog. In those days, most old people in Scandinavia didn't speak English, so we communicated with gestures and numbers. For example, she pointed to all of us, as if counting us off one by one and wrote down a total price. My parents nodded agreement. Then she made eating and drinking motions and pointed to the number "eight" on the clock, which we immediately understood to mean that breakfast would be at 8:00. Then she motioned for us to follow her upstairs, where she pointed out the bedrooms and bathroom and how the shower worked. At breakfast the next morning, other gestures and raised eyebrows communicated what we wanted to drink and whether we wanted more food. It's amazing what gestures and numbers can communicate when you don't have to convey deep thoughts.
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