Hi Rene,
You would have to set up multilingual in Joomla first, followed by in EasyBlog:
1. make your site/Joomla multilingual. This includes installing other languages, setting up the language filter plugin and language switcher module, settting up multilingual menu items. This is the documentation for Joomla multilingual setup:
link
2. Install the other languages in EasyBlog's language section
3. Enable language selection in EasyBlog composer so the blogger can choose the language:
http://take.ms/Mtjvu
This also means you have to create a few versions of a post(1 for english, 1 for spanish etc) and associate them together so when users click on the language switcher, they can switch between several language versions of the post.