When you install the translation app, the system automatically recognizes if a posted content on your community is in a language other than your community's primary language. Then the system shows you a translation sign under the content. By clicking on that sign, the system translate the content by the help of google translate.
In the example below, the primary language for the community is English. The content (answer) posted in the community is in German. So, the system suggest me to use the google to translate the answer from German to the primary language of my community, which is English in this example.