Make sure the language selector works on the lessons page.

user/themes/textbook/templates/partials/language-selector.html.twig

@@ -13,6 +13,11 @@
 {% for language in language_selector.languages %}
 
     {% set show_language = true %}
+
+    {% if uri.paths(0) == "lesson" %}
+        {% set base_lang_url = base_url_simple ~ grav.language.getLanguageURLPrefix(language) %}
+        {% set lang_url = base_lang_url ~ uri.path %}
+    {% else %}
         {% if language == language_selector.current %}
             {% set lang_url = page.url %}
         {% else %}
@@ -30,6 +35,7 @@
                 {% endif %}
             {% endif %}
         {% endif %}
+    {% endif %}
 
     {% if show_language %}
         <li>