Use KLocalizedString::languages() for language list

If ki18n >= 5.20.0 is available, use KLocalizedString::languages()
to get the list of configured languages for translations.
This fixes the lookup of translated content, such as TOCs, mirroring
what was done with commit 37bc9831fe097b01bb100f622ecd0ef19f77b80f in
kio.git.

docmetainfo.cpp

@@ -29,6 +29,7 @@
 #include "htmlsearch.h"
 #include "docentrytraverser.h"
 #include <KLocalizedString>
+#include <ki18n_version.h>
 
 using namespace KHC;
 
@@ -150,7 +151,11 @@ void DocMetaInfo::scanMetaInfo( bool force )
 {
   if ( mLoaded && !force ) return;
 
+#if KI18N_VERSION >= QT_VERSION_CHECK(5, 20, 0)
+  QStringList langs = KLocalizedString::languages();
+#else
   QStringList langs = QLocale().uiLanguages();
+#endif
   mDefaultLanguage = langs.first();
 
   QStringList::ConstIterator it;

view.cpp

@@ -12,6 +12,7 @@
 #include <KHTMLSettings>
 #include <KHTMLView>
 #include <KToolBarPopupAction>
+#include <ki18n_version.h>
 
 #include <QFileInfo>
 #include <QClipboard>
@@ -95,7 +96,11 @@ QString View::langLookup( const QString &fname )
     // assemble the local search paths
     const QStringList localDoc = QStandardPaths::locateAll(QStandardPaths::GenericDataLocation, QStringLiteral("doc/HTML"), QStandardPaths::LocateDirectory);
 
+#if KI18N_VERSION >= QT_VERSION_CHECK(5, 20, 0)
+    QStringList langs = KLocalizedString::languages();
+#else
     QStringList langs = QLocale().uiLanguages();
+#endif
     langs.append(QStringLiteral("en"));
     langs.removeAll(QStringLiteral("C"));