Sinhalese and Tamil are the two official languages of Sri Lanka, though as the country delves headfirst into the 21st century, it has begun to make a more concentrated effort to educate its population in English as a second language. Native speaking English teachers from all over the world who are TEFL or TESOL certified can find positions teaching the language to pupils of all levels, from young children to adult learners.
Most of Sri Lanka’s schools are public and state-run, though there are some private international schools where you can also look for teaching positions (these generally demand more extensive experience and qualification). The three main types of government schools where you can teach English in Sri Lanka are national schools, provincial schools, and piriven schools, which instruct Buddhist monks.
As the country begins to place a larger emphasis on higher education, you can also look for open positions teaching abroad in Sri Lanka at a local college or university as well. It’s been done before: Arthur C. Clarke, the famous science fiction writer, infamously served as the Chancellor of Moratuwa University for over two decades after emigrating from the United Kingdom.