1) Download keyboard bundle for specified language (keyboard bundle is usually in ".bundle" or ".keylayout")

2) Open Library Folder (Finder ---> Library)

3) Open Keyboard Layouts folder and drag the keyboard bundle within the folder

4) Restart the computer

5) Go to System Preference and select Language & Text

 

6) Go to Input Source and find the newly installed language

***Make sure to have the keyboard layout (in pdf) in Keyboard Layouts folder.