I just started watching "Eden of the East" and noticed that the Katakana used for Eden was エデン. I'm wondering why isn't it instead イデン which would be pronounced the same way as in English (which I was assuming was the source).
My only guess is that the source is actually something like Spanish that pronounces it differently but I have no way of checking that.
I highly doubt that they translated directly from Hebrew. The first complete translation of the bible is the [明治元訳聖書]{めいじげんやくせいしょ}, which was first published 1880. It contained already the name エデン. Before this, attempts were made to translate a Chinese versions into Japanese.
In Chinese the modern name for Eden is [伊甸]{yīdiàn}. An older name (~1875) was [埃田]{āitián}, as can be found here on the left page the 9th column from right. But the āitián is modern pinyin and I don't have any experience in Chinese language history. But I guess the pronunciation was more like エデン. In Korean for example, the pronuncation for 埃 is still 애 (~= え). And 田 is even in modern Japanese でん.
So my unsophisticated answer would be: エデン comes from 埃田 which had a similar Chinese pronunciation at that time and because people prefered to translate from Chinese instead from Hebrew/Greek original texts.
Etymology for English words can usually be found in most dictionaries, unfortunately in Japanese language dictionaries it appears that etymology usually not included.
Therefore it is probably impossible to discover the origin of the word エデン, but it is important to note that katakana is used to transliterate FOREIGN words, not just English words, and that probably at some point エデン became common usage and stayed that way. More important is to note that エデン, not イデン, if you're learning Japanese that distinction is more important than the "why" is it pronounced that way.
Just a guess, but even if the Bible had been translated from English, it could be due to the fact that someone focused on the written text of the Bible. The translator might not had heard an oral interpretation by an English native speaker at the time.
