--- a/eric6/Preferences/ConfigurationPages/EditorGeneralPage.py	Thu Oct 01 17:34:48 2020 +0200
+++ b/eric6/Preferences/ConfigurationPages/EditorGeneralPage.py	Thu Oct 01 17:39:16 2020 +0200
@@ -189,14 +189,10 @@
         """
         Private slot to add a new override entry.
         """
-        import QScintilla.Lexers
-        languages = list(
-            QScintilla.Lexers.getSupportedLanguages().keys())
+        languages = []
         for row in range(self.languageOverrideWidget.topLevelItemCount()):
             itm = self.languageOverrideWidget.topLevelItem(row)
-            language = itm.text(0)
-            if language in languages:
-                languages.remove(language)
+            languages.append(itm.text(0))
         dlg = EditorLanguageTabIndentOverrideDialog(
             editMode=False,
             languages=languages,