Gnomish

Gnomish or Gnim is the language used by gnomes, like elven, is direvated from Sylvan. Very few people except for gnome speak or understand it. Hearing gnomes talk in their native gnomish will help you realize why no one takes the time to learn it aside from gnomes. As such, gnomes now teach Common to their children to make communication with other races more productive.
However, Gnomish have a truly daunting vocabulary, with extremely fine degrees of distinction in, for example, kinds of love or shades of green. Their language was thus ideal for certain academic work,or engineering pursuits, and certain words are widely used in academic circles even among other races.