Change default language from the database?
In the setting.php file used by your site, add the following lines:

$conf['language_default'] = (object) array(
  'language' =&gt; 'en', 'name' =&gt; 'English', 'native' =&gt; 'English',
  'direction' =&gt; 0, 'enabled' =&gt; 1, 'plurals' =&gt; 0, 'formula' =&gt; '',
  'domain' =&gt; '', 'prefix' =&gt; '', 'weight' =&gt; 0, 'javascript' =&gt; ''
);


This will force Drupal to use English as default language. Once you removed the language files for that language, remove those lines from the settings.php file, or Drupal will always use English as default language, indifferently from what you set from the setting page.

The same trick works also for Drupal 6.