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();