MadMachine said:
I've looked through all the appendices and I've never found much on Elvish as a language - maybe I've got a different edition, but where is it?
The way I understand it, all of the languages Tolkien invented were Indo-European.
Taking the Elvish languages as an example he gave us a lot of both Quenya and Sindarin. I forget which is which, but one of those is an archaic, Latin-like, language. There are words in both languages he only gave examples of once, but because they are Indo-European and we have the "Latin" we can figure out what the words are in the other language.
My copy of The Silmarillion has 55 pages of appendices - Note on pronunciation, an Index of Names and Places (and their meanings), and Some Elements in Quenya and Sindarin (includes dialect and regional pronunciations and root words). Together with songs and poetry in these languages they can be reconstructed in the exact same way ancient languages are.
I couldn't be bothered going to the bookshelf to check, but the complete alphabet of at least one language and bits and pieces of others are also included in The Hobbit and LotR.
All of this goes together to enable students to study these languages as a subject that counts towards the linguistics degree at either Oxford or Cambridge (which ever one it was that Tolkien was a Prof. at), and maybe other universities, because the languages are based on the 'stern laws' of the discipline. In fact, I seem to remember reading somewhere that Quenya or Sindarin was invented by Tolkien in the first place to satisfy the requirements of his own degree in linguistics.