CB

If you accidentally click the install from directory button with no plugin directory specified it will error with the following.

Install new plugin from directory /joomla/components/com_comprofiler/plugin/ - Failed
joomla/components/com_comprofiler/plugin/default_language.php does not exist!

At which point the default language plugin is uninstalled and all translations are now missing.

http://www.joomlapolis.com/component/option,com_joomlaboard/Itemid,38/func,view/catid,146/id,149881/#149881