diff --git a/autotests/kxmlgui_unittest.h b/autotests/kxmlgui_unittest.h
--- a/autotests/kxmlgui_unittest.h
+++ b/autotests/kxmlgui_unittest.h
@@ -48,6 +48,7 @@
     void testMenusNoXmlFile();
     void testShortcuts();
     void testPopupMenuParent();
+    void testSpecificApplicationLanguageQLocale();
 };
 
 #endif
diff --git a/autotests/kxmlgui_unittest.cpp b/autotests/kxmlgui_unittest.cpp
--- a/autotests/kxmlgui_unittest.cpp
+++ b/autotests/kxmlgui_unittest.cpp
@@ -32,6 +32,7 @@
 
 #include <kedittoolbar.h>
 #include <ksharedconfig.h>
+#include <kswitchlanguagedialog_p.h>
 #include <kconfiggroup.h>
 #include <kxmlguibuilder.h>
 #include <kxmlguiclient.h>
@@ -1076,3 +1077,23 @@
     QVERIFY(popupMenu);
     QCOMPARE(popupMenu->parent(), &mainWindow);
 }
+
+void KXmlGui_UnitTest::testSpecificApplicationLanguageQLocale()
+{
+    const QLocale originalSystemLocale = QLocale::system();
+
+    KDEPrivate::setApplicationSpecificLanguage("uk");
+    KDEPrivate::initializeLanguages();
+
+    QCOMPARE(QLocale::system().language(), QLocale::Ukrainian);
+
+    KDEPrivate::setApplicationSpecificLanguage("wa");
+    KDEPrivate::initializeLanguages();
+
+    QCOMPARE(QLocale::system().language(), QLocale::Walloon);
+
+    KDEPrivate::setApplicationSpecificLanguage(QByteArray());
+    KDEPrivate::initializeLanguages();
+
+    QCOMPARE(QLocale::system(), originalSystemLocale);
+}
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -86,6 +86,7 @@
 PRIVATE
     Qt5::Network        #QNetworkAccessManager in kaboutapplicationpersonmodel_p
     Qt5::PrintSupport   #QPrinter in kshortcutseditor
+    Qt5::CorePrivate    #QSystemLocale in initializeLanguages
     KF5::CoreAddons     #KAboutData
     KF5::WidgetsAddons
     KF5::ItemViews           #KWidgetItemDelegate in KAboutApplicationPersonListDelegate
diff --git a/src/kswitchlanguagedialog_p.h b/src/kswitchlanguagedialog_p.h
--- a/src/kswitchlanguagedialog_p.h
+++ b/src/kswitchlanguagedialog_p.h
@@ -22,11 +22,16 @@
 #ifndef _KSWITCHLANGUAGEDIALOG_H_
 #define _KSWITCHLANGUAGEDIALOG_H_
 
+#include <kxmlgui_export.h>
+
 #include <QDialog>
 
 namespace KDEPrivate
 {
 
+KXMLGUI_EXPORT void setApplicationSpecificLanguage(const QByteArray &languageCode);
+KXMLGUI_EXPORT void initializeLanguages();
+
 class KSwitchLanguageDialogPrivate;
 
 /**
diff --git a/src/kswitchlanguagedialog_p.cpp b/src/kswitchlanguagedialog_p.cpp
--- a/src/kswitchlanguagedialog_p.cpp
+++ b/src/kswitchlanguagedialog_p.cpp
@@ -31,6 +31,7 @@
 #include <QSharedPointer>
 #include <QStandardPaths>
 #include <QDebug>
+#include <QtCore/private/qlocale_p.h>
 
 #include "kswitchlanguagedialog_p.h"
 
@@ -61,7 +62,12 @@
     return settings->value(qAppName(), defaultCode).toByteArray();
 }
 
-static void setApplicationSpecificLanguage(const QByteArray &languageCode)
+namespace KDEPrivate
+{
+
+Q_COREAPP_STARTUP_FUNCTION(initializeLanguages)
+
+void setApplicationSpecificLanguage(const QByteArray &languageCode)
 {
     QSettingsPtr settings = localeOverridesSettings();
     settings->beginGroup(QStringLiteral("Language"));
@@ -73,7 +79,7 @@
     }
 }
 
-static void initializeLanguages()
+void initializeLanguages()
 {
     const QByteArray languageCode = getApplicationSpecificLanguage();
 
@@ -84,14 +90,17 @@
         } else {
             qputenv("LANGUAGE", languageCode + ":" + languages);
         }
+
+        // Ideally setting the LANGUAGE would change the default QLocale too
+        // but unfortunately this is too late since the QCoreApplication constructor
+        // already created a QLocale at this stage so we need to set the reset it
+        // by triggering the creation and destruction of a QSystemLocale
+        // this is highly dependant on Qt internals, so may break, but oh well
+        QSystemLocale *dummy = new QSystemLocale();
+        delete dummy;
     }
 }
 
-Q_COREAPP_STARTUP_FUNCTION(initializeLanguages)
-
-namespace KDEPrivate
-{
-
 struct LanguageRowData {
     LanguageRowData()
     {