Det finns redan ett utmärkt svar på denna fråga av Edlothiad (jag tror inte att jag någonsin har lyckats svara på en Tolkien fråga framför honom). Eftersom frågan visar språket som en av de saker som Hobbits och dvärgar har gemensamt, vill jag lägga till lite om det.
Språket som Hobbits och dvärgar har gemensamt är inte deras eget utan snarare Westron, det språk som Dúnedain tog från Númenor, som var känt som det gemensamma talet som det var känt för alla raser.
Hober
Hobbiterna antog Westron när de migrerade norrut till Bree och Shire.
It was in these early days, doubtless, that the Hobbits learned their letters and began to write after the manner of the Dúnedain, who had in their turn long before learned the art from the Elves. And in those days also they forgot whatever languages they had used before, and spoke ever after the Common Speech, the Westron as it was named, that was current through all the lands of the kings from Arnor to Gondor, and about all the coasts of the Sea from Belfalas to Lune. Yet they kept a few words of their own, as well as their own names of months and days, and a great store of personal names out of the past.
The Lord of the Rings Prologue, Section 1: Concerning Hobbits
Page 4 (Single volume 50th Anniversary Edition)
Tidigare, när de bodde i Vales of Anduin, talade de språket för männen i den delen. Det förklarar varför Théoden känner igen ordet hobbit när han först träffar God och Pippin.
The Riders laughed. ‘It cannot be doubted that we witness the meeting of dear friends,’ said Théoden. ‘So these are the lost ones of your company, Gandalf? The days are fated to be filled with marvels. Already I have seen many since I left my house; and now here before my eyes stand yet another of the folk of legend. Are not these the Halflings, that some among us call the Holbytlan?’
‘Hobbits, if you please, lord,’ said Pippin.
‘Hobbits?’ said Théoden. ‘Your tongue is strangely changed; but the name sounds not unfitting so. Hobbits! No report that I have heard does justice to the truth.’
Merry bowed; and Pippin got up and bowed low. ‘You are gracious, lord; or I hope that I may so take your words,’ he said. ‘And here is another marvel! I have wandered in many lands, since I left my home, and never till now have I found people that knew any story concerning hobbits.’
‘My people came out of the North long ago,’ said Théoden. ‘But I will not deceive you: we know no tales about hobbits. All that is said among us is that far away, over many hills and rivers, live the halfling folk that dwell in holes in sand-dunes. But there are no legends of their deeds, for it is said that they do little, and avoid the sight of men, being able to vanish in a twinkling; and they can change their voices to resemble the piping of birds. But it seems that more could be said.’
The Lord of the Rings Book Three, Chapter 9: Flotsam and Jetsam
Page 557-8 (Houghton Mifflin Harcourt; Single Volume 50th Anniversary Edition)
dvärgar
Dvärgar har en mycket längre historia och medan de använder Westron för att kommunicera med andra människor, har de sitt eget språk som de fortfarande använder varandra.
But in the Third Age close friendship still was found in many places between Men and Dwarves; and it was according to the nature of the Dwarves that, travelling and labouring and trading about the lands, as they did after the destruction of their ancient mansions, they should use the languages of Men among whom they dwelt. Yet in secret (a secret which unlike the Elves, they did not willingly unlock, even to their friends) they used their own strange tongue, changed little by the years; for it had become a tongue of lore rather than a cradle-speech, and they tended it and guarded it as a treasure of the past. Few of other race have succeeded in learning it. In this history it appears only in such place-names as Gimli revealed to his companions; and in the battle-cry which he uttered in the siege of the Hornburg. That at least was not secret, and had been heard on many a field since the world was young. Baruk Khazâd! Khazâd ai-mânu! ‘Axes of the Dwarves! The Dwarves are upon you!’
The Lord of the Rings Appendix F, Section I The Languages and Peoples of the Third Age
Page 1132-3 (Single volume 50th Anniversary Edition)