Thank you very much, that does almost what I wanted. I made a few changes
to make the script work and then I changed it to check if the string was
already in the .php files and if it is, it uses it.
Since I don't know regular expressions and it's the first time I'm using
lisp, I guess this is a terrible code, but it works

Once again, thank you for your help.
I left here the final code I'll be using:
(defvar *ds-languages-dir* "languages")
(defvar *ds-php-file* (format "%s/pt.php" *ds-languages-dir*))
(defvar *ds-php-buffer* ())

(defun  ds-create-lang-entries ()
 "Change the selection in the current buffer and create a PHP definition in
the PHP file.
The change to make is
   \'\'
        --> \'<xsl:value-of select=\"/xml/lang/_MATCHED_STRING\" />\'.
The addition to the PHP file is made at the end of the file;
it is \'DEFINE(\"_LANG_MATCHED_STRING\", \"%s\");\'."
 (interactive)
 (ensure-php-buffer)
 (let ((xsl-format "<xsl:value-of select=\"/xml/lang/_%s\" />")
       (php-format "DEFINE(\"_LANG_%s\", \"%s\");\n")
       (oldbuf (current-buffer))
       (the-string (buffer-substring-no-properties (point) (mark))))
   (save-current-buffer
      (set-buffer *ds-php-buffer*)
      (if (search-backward the-string nil t)
        (progn
  (let ((endpoint (- (point) 4)))
    (search-backward "DEFINE" nil t)
    (let ((the-constant (buffer-substring-no-properties (search-forward
"_LANG_") endpoint)))
              ;; Change the selected text to the appropriate XSL
      (set-buffer oldbuf)
              (delete-region (point) (mark))
              (goto-char (mark))
              (insert (format xsl-format the-constant)))))
 (progn
  (set-buffer oldbuf)
            (let* ((the-constant (replace-regexp-in-string " " "_" (upcase
(read-from-minibuffer "constant: ")))))
              ;; Change the selected text to the appropriate XSL
              (delete-region (point) (mark))
              (goto-char (mark))
              (insert (format xsl-format the-constant))
              ;; <xsl:value-of select="/xml/lang/_BIG_TEXT" />
              (save-excursion
                (set-buffer *ds-php-buffer*)
                (goto-char (point-max))
                (insert (format php-format the-constant the-string)))))))))

(defun ensure-php-buffer ()
 "Make sure that everything about the PHP buffer is good."
 (unless (file-directory-p *ds-languages-dir*) (make-directory
*ds-languages-dir* t))
 (unless *ds-php-buffer* (setq *ds-php-buffer* (find-file-noselect
*ds-php-file*))))

(local-set-key "\C-c\C-c" 'ds-create-lang-entries)

On Fri, Apr 13, 2012 at 2:56 PM, Doug Lewan <dougl@shubertticketing.com>wrote:

> A concrete example always makes vague requirements clearer.
> Thank you.
>
> I think the following will do what you want.
> The process is this:
> 1. Go through the XSL buffer(s),
> 2. sweeping the strings of interest and
> 3. type C-cC-c to process.
> 4. Move on to the next string and repeat.
>
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>
> (defvar *ds-languages-dir* "languages")
> (defvar *ds-php-file* (format "%s/pt.php" *ds-languages-dir*))
> (defvar *ds-php-buffer* ())
>
> (defun  ds-create-lang-entries ()
>   "Change the selection in the current buffer and create a PHP definition
> in the PHP file.
> The change to make is
>    \'MATCHED_STRING\'
>         --> \'<xsl:value-of select=\"/xml/lang/MATCHED_STRING\" />\'.
> The addition to the PHP file is made at the end of the file;
> it is \'DEFINE(\"_LANG_MATCHED_STRING\", \"bar\");\'."
>   (interactive)
>  (ensure-php-buffer)
>   (let* ((xsl-format "<xsl:value-of select=\"/xml/lang/%s\" />")
>         (php-format "DEFINE(\"_LANG_%s\", \"bar\");\n")
>          (the-string (buffer-substring-no-properties (point) (mark)))
>         (the-STRING (upcase the-string)))
>    ;; Change the selected text to the appropriate XSL
>    (delete-region (point) (mark))
>    (goto-char (mark))
>    (insert (format xsl-format the-string))
>     ;; Now add a PHP definition at the end of the PHP file.
>    (save-excursion
>      (set-buffer *ds-php-buffer*)
>      (goto-char (point-max))
>       (insert (format php-format the-STRING)))))
>
> (defun ensure-php-buffer ()
>  "Make sure that everything about the PHP buffer is good."
>  (unless (file-directory-p *ds-languages-dir*) (make-directory
> *ds-languages-dir* t))
>  (unless *ds-php-buffer* (setq *ds-php-buffer* (find-file-noselect
> *ds-php-file*))))
>
> (local-set-key "\C-c\C-c" 'ds-create-lang-entries)
>
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>
> I hope this helps.
>
> ,Doug
>
>
>
> From: help-gnu-emacs-bounces+dougl=shubertticketing.com@gnu.org [mailto:
> help-gnu-emacs-bounces+dougl=shubertticketing.com@gnu.org] On Behalf Of
> Daniel Sousa
> Sent: Thursday, 2012 April 12 12:10
> To: help-gnu-emacs@gnu.org
> Subject: Re: Help with emacs scripting
>
> I'm majoring in applied math and computation, I know pretty well that
> computers are dumb xD
>
> I think neither of you have understood what I wanted, so I'll give you an
> example.
> I have a lot of .xsl that generate pages and I want to make those pages
> translatable. I migth have the file, for exemple, welcome.xsl:
> <?xml version="1.0" encoding="ISO-8859-1" ?>
> <xsl:stylesheet version="1.0" xmlns:xsl="
> http://www.w3.org/1999/XSL/Transform">
> <xsl:output method="html" indent="yes" encoding="iso-8859-1" />
> <xsl:template match="/">
> <xsl:if test="welcome">
> <p>Bem-vindo</p>
> </xsl:if>
> <ul>
> <xsl:for-each select="elements">
> <li>Coisa <xsl:value-of select="name" /></li>
> </xsl:for-each>
> </ul>
> </xsl:template>
> </xsl:stylesheet>
> And I wanted to make this translatable, so I change this to
> <?xml version="1.0" encoding="ISO-8859-1" ?>
> <xsl:stylesheet version="1.0" xmlns:xsl="
> http://www.w3.org/1999/XSL/Transform">
> <xsl:output method="html" indent="yes" encoding="iso-8859-1" />
> <xsl:template match="/xml">
> <xsl:if test="welcome">
> <p><xsl:value-of select="/xml/lang/_WELCOME" /></p>
> </xsl:if>
> <ul>
> <xsl:for-each select="elements">
> <li> <xsl:value-of select="/xml/lang/_STUFF" />  <xsl:value-of
> select="name" /></li>
> </xsl:for-each>
> </ul>
> </xsl:template>
> </xsl:stylesheet>
> And I create a languages/pt.php with:
>  define('_LANG_WELCOME','Bem-vindo');
>  define('_LANG_STUFF','Coisa');
>
> I have a piece of php code that puts in the xml all the constants that
> begin with "_LANG".
>
> I have a lot of these .xsl and I need to go manually through them all to
> find the strings that I want to make translatable. What I want this script
> to do is, on my input put that <xsl:value-of select="/xml/lang/_STUFF"
> /> thing on the place I select and append to the language file the
> repective define();.
>