This is a protected field that automatically displays the language in which the Translation term is written.
For example, if, when viewing the record for the term Florence, you enter Firenze as its Translation, the system will enter Italian as the language in which Firenze is written.
The system can only fill this field if you have entered a language for the Translation term. If you would like the system to fill this field and did not enter a language, save the current term anyway (with the "From" field blank) retrieve the record for the Translation term and record its language in the language field (on page one, the Hierarchy page). The system will then have the information to fill the "From" field of the original language term retroactively.
When creating the term Firenze, you may not have recorded Italian as the language of the term. Later, when viewing the record for the term Florence, you may enter Firenze as its Translation term, and notice that the system does NOT fill the "Translation From" field. Save the record for Florence anyway, retrieve the record for Firenze, enter Italian as its language and save the term. The next time you retrieve the record for the term Florence, it will be showing Italian in the "Translation From" field.