Sorry, but there are currently no built in functions available to make a character say something.
The only methods currently would be to use a value to store a string, then start a called by other action which contains a display text that is linked to the value. The other would be to use the Lua draw functions to draw the text & startAnimation function to start the talk animation of the relevant character, but to be honest neither methods are particularly practical.
Here's your first lesson in Lua, it's Lua, not LUA.
Lua is a noun, it's the Portuguese word for Moon.