To change language :
Open a text message, open the keyboard, long lick on le microphone icon and select parameters, and then you can change the input languages
or the classic , settings> Languge and keyboard>Google Keyboard(if u got stock) if not for sample "Sasmung Keyboard> (press on the keyboard settings edit" make sure u set her up
then go write message then u see in the Notification bar "Input", pick the keyboard and here u go.
normally when it dosnt show u Keyboard Lang button is cuz i didnt setup over 1 language that u need to setup in thet keyboard herself as i said above