I don't know of any way to do this during speech-to-text, but there is an option during regular typing on keyboard. If you're using Gboard, try tapping the Delete key and swiping left. If you do this during speech-to-text, the translation is terminated.
(must be enabled in Gboard -> Settings -> System -> Keyboards -> Software keyboards -> Gboard - Single-tap typing -> Gesture deletion {swipe left from Delete key to delete words}) -> on
De Funes
