By default, Track Changes is automatically on when you open a document for review or sign-off. However, when applying a translation from the TM, the content inserted into the target segment from the TM is not tracked as a change.
To turn it on:
Select File > Options. The Options dialog box is displayed.
Select Editor > Review from the navigation tree.
On the right-hand pane, under Track Changes, select when you want track changes to be automatically turned on:
When you open a document for translation.
When you open a document for review.
When you open a document for sign-off
Select Editor > Automation from the navigation tree.
On the right-hand pane, under Translation Memory, clear the check box next to the Turn off Track Changes when applying TM matches option.
Why Tracked Changes in the Source are Useful
How to Track Suggested Changes
How to Accept or Reject Suggested Target Tracked Changes
How to Display Tracked Changes Details
How to Only Display Segments with Tracked Changes