How to provide more language to choose in the gdm login screen.

[Godfrey]

Hi Ubuntu happy users,

During the login in screen, one can click the word Language at the lower left of the screen, then a list of languages are provided.  How ever I only have only one language ie English.  How do I set up the system so that it could provide more natural language to choose, such as Spanish, Gemeny, Japanese, Chinese etc.