Take a look at any map of Middle-earth and you'll find place names that fit within the world (Fornost, Ered Luin, Angmar, Minas Tirith, Mordor, Rhovanion, Erebor, Haradwaith, etc.) That seems obvious. But did you know that all of those names can be translated?
Here's the thing. Tolkien's primary profession was not author, but LINGUIST. More specifically, he was a language professor at Oxford. Tolkien loved languages -- he studied them as a hobby (look up his comments on discovering Finnish), and even invented a number of them himself...which he used as an excuse to create Arda.
Yes. The reason The Silmarillion exists is that Tolkien wanted to create a world for his made-up languages to inhabit. (The Hobbit exists because he wanted to entertain his kids, and LOTR exists because he wanted to make some money, but he managed to incorporate them into his wider legendarium.) He wanted an excuse to use Sindarin and Quenya, so he created the elves to speak them. And he didn't stop there. He gave the dwarves Khuzdul, the Dunedain Adunaic, and eventually, Westron to Middle-earth at large. (Black Speech, on the other hand, was a language he HATED, and only used when absolutely necessary. He hated it so much he didn't even let Morgoth invent it -- Sauron did that after the War of Wrath.)
In-universe, Sindarin became the lingua fraca of Middle-earth throughout the First and Second Ages, because Quenya was spoken by the Noldor, whom Thingol viewed as invaders. He and his people already spoke Sindarin anyway (they were called Sindar, so no surprises there), and would only acknowledge the Noldor if they spoke the native language. Therefore, Quenya became spoken only by the Noldor among themselves. (Side note: Tolkien didn't just invent languages, but dialects within those languages. Here's a page on Quenya on Tolkien Gateway: http://tolkiengateway.net/wiki/Quenya Note the various dialects.)
The Men of Beleriand had their own languages separate from Sindarin, although they still adopted Sindarin to speak with the elves. The House of Haleth spoke Haladin, while Taliska was spoken by the Houses of Beor and Hador. (If you've heard the word "Talkiska" before today, congratulations -- you're officially a bigger nerd than I am. I didn't learn of its existence until I started writing this, and I've been a Tolkien fan since 2001.) While the Edain's use of Taliska dwindled as the First Age wore on, they still used it enough that they were speaking it when their descendants went to Numenor, where it turned into Adunaic. When the Numenoreans returned to Middle-earth in 600 S.A., they had trouble communicating with the Men of Middle-earth because their languages had shifted over the centuries, yet they were eventually able to hold simple, broken conversations as they found there were still many similar words.
Sindarin and Quenya were still spoken in Numenor, even as Adunaic became the lingua fraca of the nation. Even in the years leading up to the Downfall, the kings and queens took Quenya names until Ar-Adunhakor forbade the use of elven languages. The Faithful, being, well, THE FAITHFUL, retained the use of Sindarin and Quenya (which is why they're known as Amandil, Elendil, Isildur, etc. -- all those names are Sindarin and not Adunaic). They kept knowledge of elven languages after their exile to Middle-earth, and went so far as to shun the use of classical Adunaic. However, despite the Dunedain's best efforts, Adunaic became more and more used as the years wore by, until, sometime in the Third Age, it became Westron, the new lingua fraca of Middle-earth.
A note of interest: Tolkien always maintained that Bilbo and Frodo, not he, were the ones who wrote The Silmarillion, The Hobbit, and The Lord of the Rings (or rather, Bilbo translated The Silmarillion from its original elvish and wrote The Hobbit, and Frodo wrote The Lord of the Rings). They wrote their versions of the books in Westron. Westron is rendered as English for the readers' benefit, but it is NOT, in and of itself, English. (Tolkien wrote his books for an English audience, but he always headcannoned...within his own writing...that he was just the one who re-discovered the books, not authored them. He was weird like that.) So: Taliska --> Adunaic --> Westron --> English.
And now we come to a point I made earlier. Sindarin was the lingua fraca of Middle-earth from the First Age onward, until it was replaced by Westron in the Third. Thanks to a thing I like to call "cultural intertia," most places retained their Sindarin names, which can be translated into Westron (as English) if the reader is so inclined.
Moria: Black Pit
Mordor: Black Land
Minas Ithil/Morgul: Tower of the Moon/Black Sorcery
Minas Anor/Tirith: Tower of the Sun/Guard (NOTE: Minas Anor/Tirith and Minas Ithil/Morgul are located in Anorien and Ithilien respectively. This is not a coincidence.)
Dol Guldur: Hill of Sorcery (NOTE: Also the hill it's located on: Amon Lanc [Bald Hill])
Angmar: Iron Home
Gondor: Stone Land
Forodwaith: Northern Waste
Haradwaith: Southern Waste (NOTE: also "gwaith", which means people -- the people are also known as Forodwaith and Haradwaith respectively, although the latter are often called Haradrim [Southern Host])
So the next time you're looking at a map of Middle-earth, take a moment to think about the name of the place you're currently looking at. There's a good chance you can translate it.
