Slow Down! Why Some Languages Sound So Fast

[S]ome languages seem to zip by faster than others. Spanish blows the doors off French; Japanese leaves German in the dust — or at least that’s how they sound.

But how could that be? The dialogue in movies translated from English to Spanish doesn’t whiz by in half the original time, after all, which is what it would have to do if the same lines were being spoken at doubletime.
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Vietnamese was used as a reference language for the other seven, with its syllables (which are considered by linguists to be very information dense) given an arbitrary value of 1.

For all of the other languages, the researchers discovered, the more data-dense the average syllable is, the fewer of those syllables had to be spoken per second — and the slower the speech thus was.