Look at the chart of world top language. You see that chinese mandarin is the first language there are about fourteen billions but english is the fourth language there are four billons. China is in asia. So i think chinese language is the best language for asean. In every countries in asean thare are a lot of chinese everywhere,there are a lot of chinese people in thailand chinese is the language for asean a lot of asean people will understand about asean better than now and look at the chart of chinese people in asean.