I can't read Malayalam messages in WhatsApp. My phone model is Sony Xperia LT28. What should I do?
The phone and the application should have Indian support along with complex scripting support. The only thing you can do is to install a Malayalam-supporting keyboard in order to type in the language. For the displaying part, you should ask the other user what he's using to type and send messages in the Malayalam language. Most likely, he's using a keyboard that's not supported by your phone.
Malayalam Keyboard: https://play.google.com/store/apps/details?id=com.patterenlogics.malayalam_keyboard