New Delhi, June 10 -- The hardest problem in simultaneous interpretation has never been vocabulary. It is timing. A human interpreter must decide, hundreds of times per minute, whether to wait for the speaker to finish a clause before translating it, or to begin speaking with partial information and risk getting the ending wrong. Google, two decades into the machine-translation business, has now published its answer to that same question - and the answer is: lean toward speed and correct as you go.

in the engineers' own framing - the trade-off between waiting for context to improve quality and translating immediately to stay in sync. That gap, a handful of seconds, is the product's defining characteristic. It is also the thing Google can...