Is this bug fixed in emacs-25? With "emacs -Q", I do not see this error
anymore. Thank you very much.

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
and is bound to "euc-jp;q=1, iso-2022-jp;q=0.5, shift_jis;q=0.5,
euc-jis-2004;q=0.5, iso-2022-jp-2004;q=0.5, utf-8;q=0.5, iso-8859-1;q=0.5,
big5;q=0.5, iso-2022-jp-2;q=0.5, gb2312;q=0.5, euc-tw;q=0.5, euc-kr;q=0.5,
us-ascii;q=0.5, utf-7;q=0.5, hz-gb-2312;q=0.5, big5-hkscs;q=0.5, gbk;q=0.5,
gb18030;q=0.5, iso-8859-5;q=0.5, koi8-r;q=0.5, koi8-u;q=0.5, cp866;q=0.5,
koi8-t;q=0.5, windows-1251;q=0.5, cp855;q=0.5, iso-8859-2;q=0.5,
iso-8859-3;q=0.5, iso-8859-4;q=0.5, iso-8859-9;q=0.5, iso-8859-10;q=0.5,
iso-8859-13;q=0.5, iso-8859-14;q=0.5, iso-8859-15;q=0.5,
windows-1250;q=0.5, windows-1252;q=0.5, windows-1254;q=0.5,
windows-1257;q=0.5, cp775;q=0.5, cp850;q=0.5, cp852;q=0.5, cp857;q=0.5,
cp858;q=0.5, cp860;q=0.5, cp861;q=0.5, cp863;q=0.5, cp865;q=0.5,
cp437;q=0.5, macintosh;q=0.5, next;q=0.5, hp-roman8;q=0.5,
adobe-standard-encoding;q=0.5, iso-8859-16;q=0.5, iso-8859-7;q=0.5,
windows-1253;q=0.5, cp737;q=0.5, cp851;q=0.5, cp869;q=0.5,
iso-8859-8;q=0.5, windows-1255;q=0.5, cp862;q=0.5, cp874;q=0.5,
iso-8859-11;q=0.5, viscii;q=0.5, windows-1258;q=0.5, iso-8859-6;q=0.5,
windows-1256;q=0.5, iso-2022-cn;q=0.5, iso-2022-cn-ext;q=0.5,
iso-2022-kr;q=0.5, utf-16le;q=0.5, utf-16be;q=0.5, utf-16;q=0.5,
x-ctext;q=0.5".