Google+ display language can be changed by using the Google Account Settings. If you are already a Google user then you would be having the right display language setting for Google Plus. But if you are new to Google then you can do the following to change your display language.
Click on the User Profile name available on the top right corner of your Google+ page. Select Account settings from the list of available options.
In the Account Settings page navigate to Language option.
This would display the following Language on the right hand side of the screen.
Now you can change the display language for your Google+ by using the Specify languages in order of preferences for viewing Google products drop down. If you want to have more than one display language for your Google Account then you can use Add another language feature. This would allow users switch from one language to another easily by making the preferred language as Primary.