Darth Vader Vs. Dark Vador!

Star War Episode III: Revenge of the Sith triumped at Cannes last night. It's supposed to be the best episode in the whole series and there are high expectations. Personally, I cannot wait to see it. but I have one question whose answer I cannot find...

The first time I ever saw a Star War movie though, it was in French and I believed the bad guy was called "Dark Vador" but later I was really susprised when finding out that (in English) it was actually "Darth Vader". Weird... isn't it?
Does anyone have any idea why the French did not keep the name? What is it like in other languages? Any idea where the name "Darth Vador" come from? It's a bit of a strange name anyway, isn't it? Does it sound like anything to English natives?

The name bears no connection with any real word except for the not-so-famous town of Vader.... which must be really scary at night!

Vader, WA (city, FIPS 73780)
Location: 46.40278 N, 122.95565 W
Population (1990): 414 (179 housing units)
Area: 2.3 sq km (land), 0.0 sq km (water)
Zip code(s): 98593
http://dictionary.reference.com/search?q=vader

UPDATE:

Thanks to kstrygg, here are some explanations:

• According to Wikipedia "Darth" may also be a portmanteau of "dark" and "death".

• Another explanation - DARTH : Title taken by Sith Lords. Early Sith Lords did not carry this title as it had not been created yet, but then later Lords took the title as they saw fit. Darth Revan is the earliest Sith Lord known to carry the title. From Darth Bane onward, all Sith Lords took the title Darth. This is also the time when the tradition of one master one apprentice began.

Yet this last one hardly explains where the word 'Darth' came from.... neither the word 'Vader'!

• DARk lord of the siTH...DARTH, a title. Also, vader just happens to be dutch for father(akin to german-vater or swedish-fader)...maybe that's just coincidence...or maybe....