Check this out from the official site, Bill Welden, from The Mythopoeic Society writes his experience down in New Zealand on set during the LOTR Production, it's a great read!

From: The Official Site

Bill Welden has been studying and writing about Tolkien's invented languages for over thirty years. He was one of several Tolkien language experts who were consulted in the making of New Line Cinema's feature film version of J.R.R. Tolkien's The Lord of the Rings. [More]