Creating a POST with url elisp package in emacs: utf-8 problem - ruby-on-rails

Question

I'm currently creating a Rest client for making blog posts much in the spirit of pastie.el. The main objective is for me to write a textile in emacs and make a post to a Rails application that will create it. It is working fine until I type anything in either spanish or japanese, then I get a 500 error. pastie.el has this same problem also by the way.
Here is the code:
(require 'url)
(defun create-post()
(interactive)
(let ((url-request-method "POST")
(url-request-extra-headers '(("Content-Type" . "application/xml")))
(url-request-data (concat "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
"<post>"
"<title>"
"Not working with spanish nor japanese"
"</title>"
"<content>"
;; "日本語" ;; not working
;; "ñ" ;; not working either
"h1. Textile title\n\n"
"*Textile bold*"
"</content>"
"</post>"))
) ; end of let varlist
(url-retrieve "http://127.0.0.1:3000/posts.xml"
;; CALLBACK
(lambda (status)
(switch-to-buffer (current-buffer)))
)))
The only way I can imagine right now that the problem could be fixed is by making emacs encode the utf-8 characters so that a 'ñ' becomes '&#241' (which works by the way).
What could be a work around for this problem?
EDIT: '*' is not equivalent to &ast;'. What I meant was that if I encoded to utf-8 with emacs using for example 'sgml-char' it would make the whole post become utf-8 encoded. Like &ast;Textile bold&ast; thus making RedCloth being unable to convert it into html. Sorry, it was very bad explained.

Answer 1

A guess: does it work if you set url-request-data to
(encode-coding-string (concat "<?xml etc...") 'utf-8)
instead?
There's nothing really to tell url what coding system you use, so I guess you have to encode your data yourself. This should also give a correct Content-length header, as that just comes from (length url-request-data), which would obviously give the wrong result for most UTF-8 strings.

Answer 2

Thanks to #legoscia I know now that I have to encode the data by myself. I'll post the function here for future reference:
(require 'url)
(defun create-post()
(interactive)
(let ((url-request-method "POST")
(url-request-extra-headers '(("Content-Type" . "application/xml; charset=utf-8")))
(url-request-data
(encode-coding-string (concat "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
"<post>"
"<title>"
"Not working with spanish nor japanese"
"</title>"
"<content>"
"日本語\n\n" ;; working!!!
"ñ\n\n" ;; working !!!
"h1. Textile title\n\n"
"*Textile bold*"
"</content>"
"</post>") 'utf-8)
)
) ; end of let varlist
(url-retrieve "http://127.0.0.1:3000/posts.xml"
;; CALLBACK
(lambda (status)
(switch-to-buffer (current-buffer))
)))) ;let