It looks as though others have been doing this for many years...
http://www.suite101.com/article.cfm/tolkien/27807
A small community of linguists devote some of their spare time to studying Tolkien's constructed languages. To some extent these languages have been growing through the years as licensees of Tolkien Enterprises and the Tolkien linguistic community have proposed new names, devised new words, or attempted to deduce roots and cognates in various dialects. These "new words" are not honest-to-goodness "J.R.R. Tolkien words", but if the wordmakers understand the rules of the languages correctly, the words are legitimate extensions of the languages, though we should perhaps envision these new word sets as defining new dialects to keep them distinct from Tolkien's dialects.
Although there are a number of very well designed Web sites which provide tutorials and basic vocabularies, the language researchers have a relatively small collection of source books to work with. Tolkien never published any formal Elvish dictionaries or grammars, but he did provide some information about the Elven languages, and his son Christopher has provided much more information.
To fully understand how the Elven languages evolved, one needs to read through the entire History of Middle-earth series. Most of the information is provided in only a few books, but there are snippets and tidbits scattered throughout them all. The history of the Elven tongues may be reduced to a few phases, however. The first phase is barely distinguishable (phonetically, in the way the words sound) from the nonsense words many present-day fantasy novels resort to for names of characters and places. They did possess what Christopher said was an underlying "sophisticated and phonetically intricate historical structure".
The names from the first phase are derived from a language Tolkien called "Qenya" and another he called "Goldogrin" (the language of the Gnomes, the race of Elves in The Book of Lost Tales whose role was given to the Noldor in The Silmarillion). He devised two lexicons (word lists or dictionaries) for these early languages.
Similarly, although I wrote about a future society, I did not invent a new language for them, other than modifying present-day words in context. It's simply a lot of work, and if one were truly successful, all the readers would have to learn the new language before reading the book.
My interest, I suppose, would lie in examining the technology and programming philosophy behind a "Universal Translator." In all likelihood, this would take the form of a robot or android who would absorb the new language most readily. Picture Anthony Daniels as C3PO.
My own androids are humanoid, for reasons we need not go into here.
Equally likely, however, is that the android interpreter will be internalized in us, as augmentations to our mental capabilities. I am currently describing this in my fourth book, developing the concepts as I work through the book. Some of you may have already read Chapter Seventeen of this forthcoming book. (Pun unintentional -- fourthcoming.)
I think Ray Kurzweil would agree with me.
I agree that there is no good purpose in writing a book in a language different from that of your intended readers - nor is any purpose served by inventing fake measurement systems, etc...
Quenya/Sindarin is a special case.
It *deserves* to be a complete language.
It just does.