Sri Lanka is a quite popular tourist country, so naturally, many Sri Lankans can communicate in English well.
Sinhalese and Tamil are the two primary languages spoken in Sri Lanka, but you’ll find that many people also speak or understand basic English. Most people who work in, or live around, major tourist destination cities like Galle, Mirissa, Weligama, Unawatuna, Colombo and Kandy will be able to communicate in conversational English. Many signs you’ll see on the street will have an English translation as well.
Though, it wouldn’t hurt to learn a few basic phrases before going to Sri Lanka: