WP 2.5 & Gettext not working

I have WP 2.5.1 running on a webhosting server, PHP 5.2.4, gettext is enabled.

When I upload a nl_NL.mo & nl_NL.po file into /wp-content/languages the blog isn’t translated.
Except for the posts that are created with the [lang_nl] & [lang_en] tags.

The wpconfig file has the locale set to NL
(‘WPLANG’, ‘nl_NL’);

For example:
In the sidebar.php I have the following code:

• <h2><?php _e(‘Language’); ?></h2>

  In the .po file I have created a translation:
  msgid “Language”
  msgstr “Taal”

  But what ever locale I use in the browser (or my blog) it’s not translated into Dutch, it remains in English…

  any ideas what I am missing?