With I8a47a8500922906bd4e4936b59b657de3bb9abdc Language::equals can
directly and faster compare the objects.
$wgLanguageCode can differ from $wgContLang->getCode() when a deprecated
language code is used. This change prevents this because Language
replaces deprecated language codes in Language::factory().
Change-Id: I07f47eceff8b3a4192278b1e9e1cfd9a41816a1c