Changing Encoding system for "Defaults for subprocess I/O"

[dan]

Hi,

When I enter "M-x eshell", the describe-coding-system shows

Defaults for subprocess I/O:
  decoding: U -- utf-8-unix (alias: mule-utf-8-unix)

  encoding: U -- utf-8-unix (alias: mule-utf-8-unix)


However, when I go to "M-x shell", it shows

Defaults for subprocess I/O:
  decoding: - -- undecided-unix (alias: unix)

  encoding: - -- undecided-unix (alias: unix)


Because of above, some international character does not show properly.

Do you know how to set the "Defaults for subprocess I/O" for all buffers/shell?

I don't know much about lisp/emacs, so specific example would be much 
preferable.

Thank you,

Dan.