You are supplied with a number of representative files from a number of different languages. It was rejected as the relative performance of different programs would be very hard to judge with realistic data.
Language recognition is a subset of pattern recognition, a large and rapidly-growing field.
The answer given below will only scratch its surface. I'm hoping to get hold of the original program and test data, which will be made available here. As a wide range of answers were acceptable, let us consider all the different factors and methods which characterise a language. We will comment in detail later. Bear in mind that the school students doing this problem will have almost no knowledge of statistics and will not know enough Maths to use the advanced classification techniques.