...
The "Diff versions" button is available when a previous version has been translated. You can click the button to see which changes have been made in the English text to understand better how much work will be involved in updating the translation. See a step-by-step guide here.
If you would like to search for all out-of-date translations at once, you can do that by running a search in Archie. Please find step-by-step instructions here.
...