The back translation translates the target text back to the original language. A back translation allows you to compare translations with the original text for quality and accuracy. Back translations help to evaluate equivalence of meaning between the source and target texts.
By default the back translation window is closed. It's available as a tab on the bottom of the translation window.
If you click on the "Back translation" tab, you will see the back translation of the target text to the original language.
You can enabled the back translation in Options to have the back translation window open.
Comparison of the back translation to the original text is sometimes used as a quality check on the original translation.
Although the back translation does not always provide the same translation result due to the asymmetric sentence structure in different languages, this feature may give you additional benefit to make sure your text is understandable.
How to enable Back Translation