The lingua franca of the NW of Middle-earth, in which the events told in the Hobbit and The Lord of the Rings took place, was called Adûni (translated as Westron), and in virtually all cases it was represented by English. The native language of the Rohirrim was related yet distinct. We know hardly anything about it apart from a few words (such as Kud-dûkan, translated as Holbytla). It was represented by Old English, aka Anglo-Saxon. Thus, an analogy is also formed about its relation with Westron.
Details are to be found in the Appendices to The Lord of the Rings.
Landroval: Kibilturg, Taurunion, Erohtar... (Watchers of Elendil)
Crickhollow: Kibilturg (Tarciryan Knights), Zigilturg (Forever Notorious), Birnavor (The Northern Kingdom)...
Visiting elsewhere as Kibilturg, Urwendil... Born and raised on Imladris