If you select a chunk of text in the page and right click there should be a context-menu option to translate the text. It's a popup with a textarea and not in-situ, but it's the same local model as far as I can tell
I believe you mean ex situ:
> By contrast, ex situ methods involve the removal or displacement of materials, specimens, or processes for study, preservation, or modification in a controlled setting, often at the cost of contextual integrity.
Might as well use the correct words if you want to talk above people's heads.
Second: The normal Firefox translate feature replaces the text in the page with the translated text - retaining its styling, position, context w/ images, etc. The right click menu, does not. I described the right click menu as "not in situ" which is correct.
I would challenge the "very common" claim.
But sure, the phrase is in use. Mostly not in tech, though.
And you are using it wrong.
If you wanted to express "in-place translation", you could have done so using your native tongue.
You're welcome.