The Identify Languages feature allows you to process extracted text/OCR to determine if there are foreign languages contained in any of your documents.
To identify languages, follow the instructions about Generating OCR/Searchable Text and make sure the "Analyze Languages" check box is checked.
You can view the progress of the language analysis process in the View Jobs interface (see Viewing Jobs for more information).
Once language analysis is complete, you will need to go to Matter -> Refresh Environment to see the Language filter options appear in Review. The "Languages" tree is nested under "More Filters" in the filter tree.