My use case: somebody used the wrong language code, “zh-hans”, to translate a page. I need to move that to “zh-cn”. The documentation doesn’t cover that case.
Topic on Help talk:Extension:Translate
OK, the way I did it is, I moved (without leaving a redirect) all of the translation-unit subpages, one by one (there can be hundreds!) and deleted the translated page with the wrong code. Then, in order to nod the Translate extension to refresh, I made a trivial edit to one of the newly moved translation units. This created a new translated page at zh-cn; however, the page has none of the history of the previous page, and the extension doesn’t allow me to restore the history entries neither by using Special:MergeHistory or by manually restoring entries. Yet another one of this extension’s many grave defects.
You could have unmarked the page for translation and moved the translation page as well.
But why is the lack of history of the translation page a grave defect?