I've tried it and actually it works great!!
Besides, it needs some improvements, let's say:
+ Language of selected text: Japanese
+ Target language: English

Currently, when I select Japanese text, it translates text to English. It's OK in this case.
But when I select English text (that is same as Target Language), and my setting for second language is FRENCH, then I have to click on the icon button on the toolbar to see the translation to FRENCH, and cannot see directly on Translation Panel.

==> IMPROVEMENT: it is expected it AUTOMATICALLY translates to SECOND LANGUAGE and directly displays on Translation Panel in case Target Language is same as language of selected text.
Many thanks.