How to increase the number of keyboard mappings beyond four?

[Avraham Hanadari]

Please forgive my duplicate posting. I thought perhaps the Subject 
heading on the original letter was unclear.

Ubuntu by default limits the number of possible keyboard mappings to
four. I'm a linguist and language hobbyist, and I really would like to
have access to more. I just learned how to enable Chinese, using the
SCIM input method. So, now I'm actually up to five. I'm sure there's a
way to tweak some system file to increase the number.  There are many 
system files which contain the word "keyboard". Can anyone tell me which 
one I'd need to edit?

Many thanks, Avraham