From the Android keyboard, press and hold the microphone button. The Input Options menu will appear with the following options: Input Languages and Google Keyboard Settings. Select the former. On the following screen, make sure that the checkbox on the top row, labelled ‘Use system language’, is not ticked.
Then, you may select one or more languages. If you enable a language that has not been used on your device, you will be alerted that the device needs to download a predictions file, therefore the device will need to be connected to the internet. Note that some languages, such as French (QWERTZ) and Russian, will change the keyboard layout and characters.