Well, nice to see you [b:2z4tl12i]GB[/b:2z4tl12i], too first off
Secondly, not all trolls are the same, and their are different races of Trolls, methinks. Perhaps there are not different Races, but there are certainly different tribes. The Trolls that Bilbo met were familiar with the ways of Men, and had many riches in Gold and Swords, and probably adapted to their surroundings, saying Men and Hobbits were close to their lairs. However, when Aragorn and Gandalf lead the Fellowship to Rivendell, you may re-call they pass by Troll Territory. These Trolls are not rich in Gold and Swords, as the other Trolls were back near the Shire, but are Vicious and it describes Bones and Skulls outside their lair.
This may be the case with Cave Trolls and Troll of Moria, that they cannot speak Common, but only their gutter-talk. And I do agree with [b:2z4tl12i]GB and others[/b:2z4tl12i] in saying that while having Arrows and Volleys shot at them, Trolls don't really have time to be having Small Talk with Gimli and Legolas