is it possible to switch languages on a page manually?
This is done by appending &amp;lcMessages=fr_FR to the URL (where fr_FR is the desired language code).

When multiple languages are enabled, there is a language switcher block that becomes enabled. What threw me off is that in Joomla that is a fixed block in the admin interface left sidebar -- but is not available to the public side of the site. In Drupal it is a block, which is more configurable. But all the language switcher does is reload the current URL with the appropriate language value.