How to open a file which name contain unicode code in Lisp(sbcl+slime)?

(with-open-file (s "~/例子.txt"
                 :external-format :utf-8)
  (print s))

result:

NIL c-string encoding error:
  the character with code 20363 cannot be encoded.
  [Condition of type SB-INT:C-STRING-ENCODING-ERROR]

Example:

in Aquamacs 3.5 with newest slime & sbcl2.0.2:

sbcl in iterm2 can do it:

Aquamacs itself can open and write filename contains utf-8 correctly, too.

I have tried to add

(setq slime-net-coding-system 'utf-8-unix)
(set-language-environment "UTF-8")

in my aquamacs config file, but it doesn't work. Please help!

Update: I have finally found the reason. When in Iterm2, the command

locale

gives this output:

While in Aquamacs open from ui, in eshell it gives:

After I added:

(setenv "LANG" "en_US.UTF-8")

to my Aquamacs config, it works! Thanks to all who reply to my question! Below is the links that helps me.

Solution

Add something like:

(setenv "LANG" "en_US.UTF-8")

to your emacs config. Explain is at above.