Not perfectly accurate, but generally well enough to do the job. I've used them with people from a variety of places around the world and found it helpful. Not enough to have a real conversation, but it's okay to relay information.
Many years ago, I worked in a university bookstore that had the ESL text contract with the school. (We were located in the international student center, so it made sense.) We had a lot of students from other countries shopping there and, as you might expect, they knew barely enough English to get by. I was often the one called over to help them, not because I knew their home language, which I definitely did not, but more because I was patient enough with them to figure out which course they were taking and therefore which book/s they needed. A translation app on my phone could have been so helpful, even if it wasn't perfect.