While both our languages divide the Order up into the two suborders Baleen Whales (Mysticeti) and Toothed Whales (Odontoceti), we Germans follow that logic and call the whole order "Whales", while you instead use an anglicized version of the scientific name (Cetacea) : Cetaceans.
We both mean the same and only use different ways to express it. (We Germans try to avoid the use of scientific names as much as possible. It's mainly a matter of spelling and keeping words short, I suspect).
Whereas we Yanks and Brits love using anglicized versions of Latin and Greek scientific names, because we think it makes us sound smarter.
And of course we Germans in recent years like to use as many english words and anglicisms as possible to sound trendy and progressive.