## If you want a non-English wiki, add a line like
$wgLanguageCode = "de";
in LocalSettings.php. But the "Startpage"
still appears in english.
If you have changed the settings after the install, then the MediaWiki
namespace is still in the language that was used during the install. You
can verify this by setting
in LocalSettings.php. If, after clearing your cache, the wiki is now in
German, the problem is that your database contains the English messages.
If you don't need the MediaWiki namespace, you can leave it at that. If
you do need it, I suggest reinstalling the wiki, but setting
$wgLanguageCode before doing so.