erp5_web_renderjs_ui: experiment base tag on launcher

bt5/erp5_web_renderjs_ui/PathTemplateItem/web_page_module/rjs_gadget_erp5_launcher_html.html

@@ -4,6 +4,7 @@
     <meta charset="utf-8">
     <meta name="google" content="notranslate">
     <meta name="viewport" content="width=device-width, initial-scale=1">
+    ${extra_base_tag}
     <link rel="shortcut icon" href="favicon.ico">
     <meta name="theme-color" content="#085078">
 

bt5/erp5_web_renderjs_ui/SkinTemplateItem/portal_skins/erp5_web_renderjs_ui/WebSection_renderDefaultPageAsGadget.py

@@ -65,6 +65,12 @@ if configuration_webapp_manifest_url is None:
 else:
   mapping_dict["webapp_manifest_full_link_tag"] = '<link rel="manifest" href="' + configuration_webapp_manifest_url + '">'
 
+# base tag
+if mapping_dict["default_selected_language"] == default_language:
+  mapping_dict["extra_base_tag"] = ""
+else:
+  mapping_dict["extra_base_tag"] = '<base href="../">'
+
 # Wallpaper
 # It can not be done in Javascript, due to CSP protection.
 # data- attribute can not be accessed outside the content property