You will be able to associate your post with a language on your site. This is useful when you plan to have multi lingual content on a single website. To set this up, you need to follow the instructions below:
Ensure that you have already setup multi lingual support on your Joomla site. You may refer to the guide at Setting up Multilingual Site in Joomla 3.
If multi lingual support is already setup on the site, you will be able to associate the post as a primary language as shown below:
Then, you may choose association of other posts as different language by clicking on the
Select Postbutton shown above. Clicking on that button would display a popup allowing you to pick a post:Save the post and you are good to go. When viewing the post on the front end, switching language using the language switcher will redirect the user to it's alternative post in a different language.

