In J.R.R. Tolkien’s fiction, the Dwarves speak Khuzdul.
Khuzdul is the secret language of the Dwarves of Middle-earth. Tolkien presented it as a language developed by the Dwarves themselves, distinct from the tongues commonly used in trade or by neighboring peoples. The Dwarves generally guarded it closely, so relatively little Khuzdul appears in the published stories.
The name Khuzdul comes from the Dwarves’ own word for their language. It is sometimes confused with the languages Tolkien created for Elves, especially Quenya and Sindarin. Those Elvish languages have much more extensive surviving vocabulary and grammar, while Tolkien left Khuzdul comparatively limited in the published works.