You can download all available languages for free then follow the below instructions to install them into your mooSocial site.

Download all available languages

How to Install language 

• Unzip the languages.zip (downloaded from link above)
• Upload app folder from extracted languages folder to your app folder on server
• Goto Admin Dashboard >>> Site Manager >>> Languages Manager
• Choose tab Not install Languages  and find the uninstall language that you want to install click install.
• Go to Admin Dashboard >>> Clear Global Caches