There may be an easier way than this, but this is what I've done so I can type in different languages/alphabets.
Go into the System Preferences.
Click on the International control panel.
Click the Input Menu tab.
Select all the languages you want to be able to type in.
Once there's 2 or more languages selected, a menu should appear to the right of the Help Menu at the top of the screen that allows you to select which language to type in.
Depending on the languages you selected, there should be an option to show the character palette, and you can use that to type in characters, or learn which keys on your keyboard do what for the new language.