Multilingual support
i think you are right that there is not a lot of information about this currently. Multiple language can be enabled on the Localisation screen ie at http://d46.demo.civicrm.org/civicrm/admin/setting/localization?reset=1

Some documentation about it is here 
http://gitbook.civicrm.org/the-civicrm-community/localising-civicrm.html
http://wiki.civicrm.org/confluence/pages/viewpage.action?pageId=88408149

Once multiple languages have been enabled, when you are creating eg a Contribution Form you should see new green buttons next to fields that will allow you to provide a translation of the text.

NOTE: we have had issues when trying to run CiviCRM with more than 2 or 3 languages so you need to test this on a dev site of course. 

RANDOM IDEA: I haven't thought about this previously but if you are using Drupal then there may be options to provide alternative language versions of a webform_civicrm form that is connected to your Member Form