diff --git a/src/core/CMakeLists.txt b/src/core/CMakeLists.txt
--- a/src/core/CMakeLists.txt
+++ b/src/core/CMakeLists.txt
@@ -32,7 +32,9 @@
   REQUIRED_HEADERS SonnetCore_HEADERS
 )
 
-target_link_libraries(KF5SonnetCore PUBLIC Qt5::Core)
+target_link_libraries(KF5SonnetCore
+                      PUBLIC Qt5::Core
+                      PUBLIC Qt5::Widgets)
 
 set_target_properties(KF5SonnetCore PROPERTIES VERSION ${SONNET_VERSION_STRING}
                                                SOVERSION ${SONNET_SOVERSION}
@@ -63,6 +65,8 @@
             ${SonnetCore_HEADERS}
         LINK_QCHS
             Qt5Core_QCH
+            Qt5Gui_QCH
+            Qt5Widgets_QCH
         BLANK_MACROS
             SONNETCORE_EXPORT
             SONNETCORE_DEPRECATED_EXPORT
diff --git a/src/core/loader.cpp b/src/core/loader.cpp
--- a/src/core/loader.cpp
+++ b/src/core/loader.cpp
@@ -30,6 +30,7 @@
 #include <QPluginLoader>
 #include "core_debug.h"
 #include <QDir>
+#include <QMessageBox>
 
 #include <algorithm>
 
@@ -86,14 +87,29 @@
     QString backend = clientName;
     QString plang = language;
 
+    const QString &defaultLang = d->settings->defaultLanguage();
     if (plang.isEmpty()) {
-        plang = d->settings->defaultLanguage();
+        plang = defaultLang;
     }
     const QVector<Client *> lClients = d->languageClients[plang];
 
     if (lClients.isEmpty()) {
-        qCWarning(SONNET_LOG_CORE) << "No language dictionaries for the language:" << plang;
-        return nullptr;
+        if (plang == defaultLang) {
+            const QString localeLang = QLocale::system().name();
+            if (d->settings->setDefaultLanguage(localeLang)) {
+                d->settings->save();
+                QMessageBox::information(nullptr,
+                                         tr("Spell Checker"),
+                                         tr("No dictionaries for language: \"%1\" could be loaded.\n"
+                                            "The default dictionary has been reset to the system locale: \"%2\"").arg(plang).arg(localeLang));
+            } else {
+                qCWarning(SONNET_LOG_CORE) << "No language dictionaries for language:" << plang << "or locale language:" << localeLang;
+                return nullptr;
+            }
+        } else {
+            qCWarning(SONNET_LOG_CORE) << "No language dictionaries for language:" << plang;
+            return nullptr;
+        }
     }
 
     if (backend.isEmpty()) {
diff --git a/src/core/sonnet-core.pro b/src/core/sonnet-core.pro
--- a/src/core/sonnet-core.pro
+++ b/src/core/sonnet-core.pro
@@ -1,7 +1,7 @@
 TARGET = sonnet-core
 TEMPLATE = lib
 CONFIG += staticlib c++11
-QT -= gui
+QT += widgets
 
 SOURCES += loader.cpp \
            client.cpp \