bind_textdomain_codeset

First the the url of the gettext manual changed:
http://www.gnu.org/software/gettext/manual/
Secondly, lets explain a little bit what this fonction does.
By default, gettext will use the LC_CTYPE of the language you choose (for example fr_FR).
This LC_CTYPE is extracted from your locales.alias file in your configuration dir (Should be /etc/locales.alias).
By default, the encoding is frequently iso-8859-1.
So if you want to make your site utf-8 aware, you need to bind your domain with the right encoding.
Here is a sample:
<?php
 $locale="fr_FR.UTF-8"
 setlocale(LC_MESSAGES, $locale);
 $domain = 'your_text_domain';
 bindtextdomain($domain, './translations_path');
 textdomain($domain);
 bind_textdomain_codeset($domain, 'UTF-8');
?>

As quoted in other notes, the translations path should be like
/translations_path
 /de_DE/
 /LC_MESSAGES
 /fr_FR/
 /LC_MESSAGES
 ...
Your translation goes in the LC_MESSAGES dirs ... Hopes this helps :)

I had problems with German "umlauts" when using gettext. So, this is how it can be resolved:
I've put these lines itom my PHP code:
$domain = "messages";
bindtextdomain($domain, "path_to_messages_dir");
bind_textdomain_codeset($domain, 'ISO-8859-15');
textdomain($domain);
It works!

So, by using this function and by setting the LANGUAGE variable, you should be able to have a functioning i18n system that is not dependent upon a system's locale installation. Here is a sample from a method I created for a language class. Look for it on http://wiki.creativecommons.org/Developer soon:
 function Init ()
 {
 // set the LANGUAGE environmental variable
 // This one for some reason makes a difference FU@#$%^&*!CK
 // and when combined with bind_textdomain_codeset allows one
 // to set locale independent of server locale setup!!!
 if ( false == putenv("LANGUAGE=" . $this->_language ) )
 CCDebug::Log(sprintf("Could not set the ENV variable LANGUAGE = %s",
 $this->_language));
 // set the LANG environmental variable
 if ( false == putenv("LANG=" . $this->_language ) )
 CCDebug::Log(sprintf("Could not set the ENV variable LANG = %s",
 $this->_language));
 // if locales are not installed in locale folder, they will not
 // get set! This is usually in /usr/lib/locale
 // Also, the backup language should always be the default language
 // because of this...see the NOTE in the class description
 // Try first what we want but with the .utf8, which is what the locale
 // setting on most systems want (and is most compatible
 // Then just try the standard lang encoding asked for, and then if
 // all else fails, just try the default language
 // LC_ALL is said to be used, but it has nasty usage in some languages
 // in swapping commas and periods! Thus try LC_MESSAGE if on one of
 // those systems.
 // It is supposedly not defined on WINDOWS, so am including it here
 // for possible uncommenting if a problem is shown
 //
 // if (!defined('LC_MESSAGES')) define('LC_MESSAGES', 6);
 // yes, setlocale is case-sensitive...arg
 $locale_set = setlocale(LC_ALL, $this->_language . ".utf8",
 $this->_language . ".UTF8",
 $this->_language . ".utf-8",
 $this->_language . ".UTF-8",
 $this->_language,
 CC_LANG);
 // if we don't get the setting we want, make sure to complain!
 if ( ( $locale_set != $this->_language && CC_LANG == $locale_set) ||
 empty($locale_set) )
 {
 CCDebug::Log(
 sprintf("Tried: setlocale to '%s', but could only set to '%s'.", $this->_language, $locale_set) );
 }
 $bindtextdomain_set = bindtextdomain($this->_domain,
 CC_LANG_LOCALE . "/" . $this->_locale_pref );
 if ( empty($bindtextdomain_set) )
 CCDebug::Log(
 sprintf("Tried: bindtextdomain, '%s', to directory, '%s', " .
 "but received '%s'",
 $this->_domain, CC_LANG_LOCALE . "/" . $this->_locale_pref,
 $bindtextdomain_set) );
 bind_textdomain_codeset($this->_domain, "UTF-8");
 $textdomain_set = textdomain($this->_domain);
 if ( empty($textdomain_set) )
 CCDebug::Log(sprintf("Tried: set textdomain to '%s', but got '%s'",
 $this->_domain, $textdomain_set));
 } // end of method Init ()