How does the author use language in the Unfinished Tales of Numenor and Middle-earth?

One important facet that makes reading Tolkien more interesting than some other writers is the fact that he has made up his own language. In the realm of Middle Earth, each of the main races of creatures have their own language. As a reader, it can be confusing to keep the different terms straight with their meanings and language. It is helpful that the collection comes complete with a full index to define the terms and phrases used. While on the one hand it can be hard to remember which terms come from which race, it does bring a new level of detail to the stories. It is also a testament to Tolkien's skill and dedication to the integrity of his world that the words and meaning are the same from tale to tale.