Created module and base implementation

iq_lang_switcher.info.yml

@@ -0,0 +1,6 @@
+name: iQual Language Switcher Improvements
+description: Disables inactive languages in front end.
+package: Custom
+
+type: module
+core: 8.x

iq_lang_switcher.module

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+<?php
+function iq_lang_switcher_language_switch_links_alter(array &$links, $type, $path)
+{
+    if (\Drupal::currentUser()->hasPermission('bypass node access')) {
+        return;
+    }
+    if ($node = \Drupal::routeMatch()->getParameter('node')) {
+        $translations = $node->getTranslationLanguages(true); 
+        foreach ($links as $langcode => $link) {
+            if ($node) {
+                if (array_key_exists($langcode, $translations)) {
+                    $translation = $node->getTranslation($langcode);
+                    if (!$translation->isPublished()) {
+                        unset($links[$langcode]);
+                    }
+                } else {
+                    unset($links[$langcode]);
+                }
+            }
+        }
+    }
+}