For a board with multiple language packs installed, at the Registration page, you can switch between languages on-the-fly via pull-down menu.
Switching languages, however, does not work for extensions, even if the extension has translations for the other languages.
When switching to a new language, any extension text on the registration page (i.e.: Header nav links) resort to displaying as raw language variables.
Also, switching back to English, the extension language variables remain as raw lang vars.