Language switcher give 404
Solution was here : https://drupal.stackexchange.com/a/150657/8753

For D6 the path is : admin/settings/language/edit/en

No need to set the prefix into the URL provided by pathauto here : admin/build/path/pathauto

in admin/settings/language/configure , both choice between Prefix only or Prefix and alternative solution seem to work.