There is a small but steadily increasing demand for learning English in Sri Lanka and it is promoted by the government as a means of communication between different enthnic groups. Therefore, we would expect to see a greater demand for teachers, particularly both the paid and the voluntary sector. However, you are more likely to find paid work in Singapore, Malaysia, Thailand and Brunei and there is a growing industry in Vietnam and Cambodia also.
English is commonly used in government but spoken competently by only about 10% of the population. However, there is a big market for Sri Lankans wishing to train as online English teachers and this might also be an avenue you consider to cover any gaps in paid employment.
will both be helpful courses for you if you wish to teach English in Sri Lanka.