Currently a translation cannot be removed, you will end up with an empty caption.
Especially with captions which only have replacement values and no literal text, it can be useful to reset the caption because Mendix likes to put in a default, which you would have to replace with, for example, {1} - {2}.
Nobody will expect that a caption with only replacement values actually has a translation. When there are no literal texts, the value will usually be the same regardless the user language.
As this might be difficult to do in the propery editor and it is a bit of an edge case, a button in the batch translate popup to reset the translation would be just fine.