diff --git a/src/core/loader.cpp b/src/core/loader.cpp
--- a/src/core/loader.cpp
+++ b/src/core/loader.cpp
@@ -89,13 +89,18 @@
     if (plang.isEmpty()) {
         plang = d->settings->defaultLanguage();
     }
-    const QVector<Client *> lClients = d->languageClients[plang];
 
-    if (lClients.isEmpty()) {
+    // make sure plang is one of languages(), otherwise calling
+    // d->languageClients[plang] will create a default-constructed value
+    // for it and it doesn't have any dictionaries to begin with
+    if (!languages().contains(plang)) {
         qCWarning(SONNET_LOG_CORE) << "No language dictionaries for the language:" << plang;
+        emit loadingDictionaryFailed(plang);
         return nullptr;
     }
 
+    const QVector<Client *> lClients = d->languageClients[plang];
+
     if (backend.isEmpty()) {
         backend = d->settings->defaultClient();
         if (!backend.isEmpty()) {
diff --git a/src/core/loader_p.h b/src/core/loader_p.h
--- a/src/core/loader_p.h
+++ b/src/core/loader_p.h
@@ -127,6 +127,14 @@
      */
     void configurationChanged();
 
+    /**
+     * Emitted when loading a dictionary fails, so that Ui parts can
+     * display an appropriate error message informing the user about
+     * the issue.
+     * @since 5.55
+     */
+    void loadingDictionaryFailed(const QString &lang) const;
+
 protected:
     friend class Settings;
     void changed();
diff --git a/src/ui/dictionarycombobox.h b/src/ui/dictionarycombobox.h
--- a/src/ui/dictionarycombobox.h
+++ b/src/ui/dictionarycombobox.h
@@ -109,6 +109,8 @@
 private:
     DictionaryComboBoxPrivate *const d;
     Q_PRIVATE_SLOT(d, void slotDictionaryChanged(int))
+
+    void slotLoadingDictionaryFailed(const QString &lang);
 };
 }
 
diff --git a/src/ui/dictionarycombobox.cpp b/src/ui/dictionarycombobox.cpp
--- a/src/ui/dictionarycombobox.cpp
+++ b/src/ui/dictionarycombobox.cpp
@@ -19,6 +19,9 @@
 */
 
 #include "dictionarycombobox.h"
+#include "loader_p.h"
+
+#include <QMessageBox>
 
 #include <speller.h>
 #include "ui_debug.h"
@@ -34,6 +37,7 @@
 
     DictionaryComboBox *q;
     void slotDictionaryChanged(int idx);
+    bool dictionaryErrorShown = false;
 };
 
 void DictionaryComboBoxPrivate::slotDictionaryChanged(int idx)
@@ -48,6 +52,8 @@
     : QComboBox(parent)
     , d(new DictionaryComboBoxPrivate(this))
 {
+    connect(Loader::openLoader(), &Loader::loadingDictionaryFailed,
+            this, &DictionaryComboBox::slotLoadingDictionaryFailed);
     reloadCombo();
     connect(this, SIGNAL(activated(int)),
             SLOT(slotDictionaryChanged(int)));
@@ -140,6 +146,17 @@
     }
 }
 
+void DictionaryComboBox::slotLoadingDictionaryFailed(const QString &lang)
+{
+    if (!d->dictionaryErrorShown) {
+        QMessageBox::warning(nullptr,
+                                 tr("Spell Checker"),
+                                 tr("No dictionaries for language: \"%1\" could be loaded.\n"
+                                    "Please check the spell checker configuration.\n").arg(lang));
+        d->dictionaryErrorShown = true;
+    }
+}
+
 } // namespace Sonnet
 
 #include "moc_dictionarycombobox.cpp"