Feature 1451 : localization with gettext

Use php-gettext (developpement version rev43, because of php5.3) as fallback
Use native language (english) instead of key for translation
Keep directory en_UK for english customization
Need some refactoring for plurals

Todo : managing plugins in the same way

git-svn-id: http://piwigo.org/svn/trunk@5021 68402e56-0260-453c-a942-63ccdbb3a9ee

admin/extend_for_templates.php

@@ -146,7 +146,7 @@ WHERE param = 'extents_for_templates';";
   if (pwg_query($query))
   {
     array_push($page['infos'], 
-      l10n('Templates recorded.'));
+      l10n('Templates configuration has been recorded.'));
   }
 }