Not sure if this requires errata or not, but it could--and it definitely needs some clarification, in either case.
Page 25, PHB, it says that you cannot learn Abyssal or Supernal as a 1st-level character. Does this apply even to people who take the Linguist feat, or does it refer only to those languages you automatically gain at 1st level? (Some races, such as humans and halflings, gain "Common plus one other.")
It seems to me that, once you've gone through the "expense" of the feat, you should have the option of taking those languages, since they won't break anything at 1st that they wouldn't at 2nd. (And since I'm pretty sure the point of the 1st-level restriction is to make sure you have to spend a feat to gain those languages.) But by a RAW reading, that's not what it says; the strictest interpretation would have it that, if you buy the Linguist feat at 1st level, you still can't learn 'em.