[Feature Request] Implement 2 missing features on translation panel

[jaejunks]

1. Include a pulldown for the source language which include the "auto detect" option (as the default option); for manual source language selection. Because sometime the translation engine incorrectly detects the source language.

2. If the source language is auto detected, also display the detected source language; or adjust the selected option in the source language pulldown. So that we can know whether the translation is correct or not, and also to provide a hint of the inputted language.

Thank you.