As per my practical experiance:
I18N: Suppose your OS is English(US),You can just change the OS language to Japanese/Chineese and can Install application in either Japanese/Chineese support.
L10N:Your OS must be in the same locale as the application.eg on Japanese OS you can install Japanese language supported application.Here every thing will be in the same lacale.
G11N: Its a naming conversion given by IBM/Sun Microsystem.It covers both I18N & L10N based on type of all setting.
Correct me if I am wrong.
Thanks
Vikas