I've always been puzzled at the origin of the translation of "George" into Chinese. It's probably the only (pardon me if there are more) name that does not sound like its English counterpart.
About the "乔" part of "George[dʒɔ:dʒ]", you can find some material in the 译音表(the Form of Ttransliteration). Besides, "奇" should be instead of "治" following the form.
However, "约定俗成(the convention)" is one of the important rules of 《英文人名翻译准则》. Everybody often use "乔治" refer to "George", so that "乔治" is agreed upon gradually. Anyway, I don't know why did the first person call "George" "乔治".
Some says that "乔治" is very close to George in Shanghainese (上海話) since Shanghai was the big harbor allows international trades in 17th century. Lots of phrases are created/translated at that time. http://en.wikipedia.org/wiki/Chinese_Pidgin_English
No, it is not the only one.
Unless you think John sounds similar to 约翰.
Chinese translations for foreign names and words (such as names of other stuff) are weird if you compare them to each other. People from the cities, Guangzhou, Hong Kong (Speaking Cantonese), and Shanghai (Speaking Wu), which were first open to the world, created these translations based on their dialect.
Examples (Some of them have been used for such a long time that native speaker as me would not notice that they are not original Chinese words):
Sandwich 三明治 Toast 吐司 Cookie 曲奇 Humor 幽默 (I thought it is originally Chinese) Taxi 的士 Pancake 班戟 Chocolate 巧克力/朱古力
Note that one word may have more than one translations.
When I did an immersion at UC-Berkeley a long time ago I was told my name, George, had the equivalent 乔治 Qiáozhì because that name was already established in school books for George Washington. It always sounded to me closer to the French Georges. My family name is Lang and I was given the choice between forest 林 Lín or blue 蓝 Lán. I chose the former, for obvious reasons of stroke number.