Why the different pronunciation of "Ra's?" Some pronounce it like it rhymes with "was" while others (including Ra's himself) seem to pronounce it "Raash" with a long A sound. You would think that by now they would have standardized the pronunciation, unless they deliberately wanted the differences.
The official explanation:
http://deadline.com/2015/04/the-flash-wondercon-arrow-cw-1201404723/
On a final, humorous note, a lingering continuity issue that has bedeviled fans of The Flash sister show Arrow was also cleared up during the panel. Asked during the fan Q&A segment why the name of villain Ra’s al Ghul is sometimes pronounced as “rahs”, while other times as “Raysh”, Kreisberg confirmed this was intentional.
“Most of us comic-book fans, we call him ‘Raysh’, not ‘Rahs'” he told the crowd. But, he said, director Christopher Nolan‘s decision to pronounce the name as “Rahs” in Batman Begins led to confusion among casual fans. Therefore, “what we decided is that if you’re [allied with the character], you call him ‘Raysh’, and if not, you call him ‘Rahs.'”