It just mentions that they have a unique language and some have learned it and used it to calm them.
I've wondered if there is an aedric language counterpart to the daedric spoken in Oblivion, if there is I'd expect that spriggans and other nature spirits would use variations of it.
"It is a lovely language, but it takes a very long time saying anything in it, because we do not say anything in it, unless it is worth taking a long time to say, and to listen to." - Treebeard