Try recreating this example. Post a Tweet with
"setting up my twitter 私のさえずりを設定する".
* Put "status=setting%20up%20my%20twitter%20私のさえずりを設定する" in
the POST body.
* The Base String *must* have (case-sensitive, etc) :
status%3Dsetting%2520up%2520my%2520twitter%2520%25E7%25A7%2581%25E3%2581%25AE%25E3%2581%2595%25E3%2581%2588%25E3%2581%259A%25E3%2582%258A%25E3%2582%2592%25E8%25A8%25AD%25E5%25AE%259A%25E3%2581%2599%25E3%2582%258B
in it.
Please confirm that you are getting the same values. If you do not, you
should look at how you encode UTF8 data.
Tom