Starbuck_II
Explorer
Really, I find Undercommon to be a (pardon the pun) common language to take.The third problem is language. Roper speaks Terran and Undercommon. It often happens that no-one in the party can speak those languages. Unless the party mage has a scroll of Comprehend Languages ready (unlikely), many parties cannot negotiate with it even if they want.
I mean, at least 1/3rd of the world speaks it (almost all underground do: Mindflayer, Drow, etc).
I'll admit I never though to talk to a Roper though.