@Jearick. I don't know if there is right or wrong or a definitive answer to your question. I like Lynnjuniper's idea of speech quirks for characters from a different race but would say that each player should have the freedom to come up with his/her own than be limited by someone else's ideas. Your PC, Tath, for instance, has a far more unique and interesting 'sound' for the accent you have given him than if you had been told, 'he should talk like xyz'.
Additionally, nurture over nature would be more influential in determining accent where anatomical issues are not at work I guess. Much like people in RL, Dark Elves from two far distant areas might very well have entirely different accents. The RP you come up with of why s/he speaks this way in particular is a lot more fun than any generic reason you might be given.
Having said that, I always 'hear' in my mind a really nasty sibilant sound, full of unspoken menace and venom when I read the drow or dark elf tongue being spoken from various sources.
But that's just me!
