In almost every source I know, Euler has been pronounced as /ˈȯi-lər/ . Nevertheless, in a number of books translated to other languages, it is mentioned as: /ˈjuːlər/ . I doubt in it incorrectness, but have not found any source to prove it. Is this pronunciation correct or not?

Furthermore, pronouncing the word Leonhard, are we supposed to say the h letter, too?

- Thank you in advance

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    The German pronunciation of eu is /oi/ and the h of Leonhard is pronounced. But there is no rule how you have to pronounce foreign names. Yet in mathematic circles I think the pronunciation of Euler is with /oi/. – rogermue Mar 26 '16 at 7:56
  • He was German-speaking Swiss so the pronunciation of his name isn't really on-topic here. English Wikipedia is correct according to how I was taught, but it's not surprising that some tests translated from English get it wrong. – Chris H Mar 26 '16 at 8:09
  • You pronounce it the way Leonhard pronounced it. – Hot Licks Mar 26 '16 at 12:44
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    @HotLicks: since Leonhard probably spoke 18th century Swiss German, it's quite likely even the Germans today don't pronounce his name the way Leonhard pronounced it. :-) – Peter Shor Mar 26 '16 at 14:29
  • What @rogermue said. – Drew Mar 26 '16 at 17:21

In 1905, according to the Century Dictionary, Eulerian was pronounced /juˈliːrɪən/ (rhyming with Shakespearian). So presumably, in 1905 Euler was pronounced /ˈjuːlər/. (Yooler, for those who can't read IPA.)

The English-speaking mathematical community has long since realized the error of its ways, and started pronouncing Euler's last name using the modern German pronunciation, /ˈɔɪ.lər/. We still usually leave out the /h/ in his first name, and put a /d/ on the end. (The German pronunciation is more like /leːɔnhart/.) But from the OP's comments, this newer pronunciation has not spread to other languages that borrowed the English pronunciation when it was still Anglicized.