Nice plugin if you only want to change content, but Joomla supports already content in multiple languages.

Multilingual category names, or components that don't support multiple languages, are not considered by this plugin.

Right, this is only simple supporting plugin for content supporting "onContentPrepare" event. Out of box it can be used in content articles and/or in custom modules.
However, if you need to translate menu items, titles of articles / categories etc. it can be done by modifying template, adding HtmlHelper::_('content.prepare') call.