I've reproduced this at least three times in the evening when I reported it, but didn't ever since. It's possible that it had indeed completed, and the debug tool from Chromium failed to notice. Right now, I get a response for that particular xhr, albeit after a full 7 second delay.
My problem is, however, that when loading the translation for https://ro.wikipedia.org/wiki/Special:ContentTranslation?title=Special:ContentTranslation&campaign=contributionsmenu&to=ro&page=Norway&from=en&targettitle=Norvegia&revision=741251081 I get the translated content (right side column) greyed out and not editable. The article is translated almost all the way through, but the infobox is not, and I intend to leave it that way. The three-dots "pending" animation is showing next to where the translated infobox is supposed to be (but isn't and shouldn't be). I have no idea why the editor refuses to activate, after all XHRs have finished. If I click on paragraphs at the left, they are added to the translation, but I cannot edit them.
And all of this happens all the time, regardless of whether or not XHRs are reported as finished by the debug console.
They gray color might come from a disabled class. The only place in the code I can find that is the edit conflict warning, and that does it for all columns, which is not the case here.
In this case, it looks like that restoration has failed using the latest version, so it has loaded an older version (revision parameter in the url). It seems that version succeeded to restore, given it says "saved just now" at the top.
I think I have something that may help you investigate the issue at hand: I managed to unblock the Norway translation. Seems to be associated with the fact that one of the templates used in the translation did not have TemplateData (in my case, Convert), but was connected via Wikidata to a template in the original. After adding the templatedata, I got a translation that's still messed up, but editable.
I got to this by checking the list of requests made by the browser. The last one was a request to convert a template to wikitext. I looked in the source language wikitext, and saw that both that template, and the next template, Convert, were missing templatedata. After I filled in the templatedata for both of these templates, it works. The first one seemed to be successful, so wasn't much of a bother, but I suspect the Convert was problematic.
I think the title of the issue can be changed.