The most quoted fact about Darth Vader is that his name is Dutch for "dark father." Lucas did say something close to that. He also said other things.
In a Rolling Stone interview in June 2005, Lucas put it plainly: "Darth is a variation of dark. And Vader is a variation of father. So it's basically Dark Father." The linguistics hold up on the second half. Etymonline lists Dutch vader and German Vater among the Germanic relatives of English father, all from a root that also gave Latin and Greek pater.
The trouble is timing. That explanation arrived almost three decades after the first film. A writer at File 770 called it "somewhat spurious," because Darth Vader was not always meant to be the character we now know. A Slashfilm history of the drafts says he was in the 1975 second draft, already much as he would look on screen.
Whether Lucas always meant Vader to be Luke's father is contested. Mental Floss reports that Lucas has said the Skywalker family drama was always part of his plan. It adds that other accounts say it was not settled until work on The Empire Strikes Back was well underway. If the father idea came later, the "dark father" reading would be a lucky fit rather than a design.
Lucas has given other origins too. On one occasion he said the name grew out of the phrase "dark water." Wikipedia also notes that a boy called Gary Vader went to high school with him, which may be where the surname came from.
So the honest verdict is disputed. The name sounds like dark, and in Dutch it means father. Whether that was the plan in 1975 or a gloss added later depends on which Lucas interview you trust.
Other countries reshaped the name entirely. French audiences have known him as Dark Vador since 1977. Italian versions used Dart Fener, chosen again by a fan vote in 2004. In Icelandic he is Svarthöfði, which Wikipedia translates as "black-head."