Automatically select translation-from language to the page's lang parameter

[michaelnordmeyer]

Currently the translation dialog will have the first language selected when the dialog is displayed, or the last selected one.

I'd like to have it to automatically select the language the response has attached to it in the lang parameter, if there is one and if it's a translatable language.

[skyjake]

v1.15.5 added "Auto-detect" as the default source language. This is LibreTranslate's autodetection and does not check the MIME lang.

There is still some value in checking lang because LibreTranslate may not always choose the right language. However, in the wild, lang seems relatively rare so given the new autodetection working in most cases, implementing this is pretty low on the priority list.