> I guess we need to run url-mime-charset-string through
> url-http--encode-string as well.  Can you try that?

Yes. I attached a patch.

2016-08-13 16:02 GMT+09:00 Eli Zaretskii <eliz@gnu.org>:
> From: Sho Takemori <stakemorii@gmail.com>
> Date: Sat, 13 Aug 2016 09:30:35 +0900
> Cc: Eli Zaretskii <eliz@gnu.org>, larsi@gnus.org, schwab@linux-m68k.org,
>       24117@debbugs.gnu.org
>
> But I set the language environment by (set-language-environment "Japanese") in ~/.emacs.d/init.el.
> With the configration, I still see the same error when using anaconda-mode.
>
> And url-mime-charset-string in url-http-create-request is a multibyte stirng

I guess we need to run url-mime-charset-string through
url-http--encode-string as well.  Can you try that?

Thanks.