h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Quenya is not the dialect of High Elves. The High Elven language is Sindarin, which is mostly used for ceremonial purposes. Quenya is the conversational dialect of Elvish.

I quote "The Lord of the Rings": Appendix F - The Languages and Peoples of the Third Age.

"Of the Eldarin tongues two are found in this book: the High-elven or Quenya, and the Grey-elven or Sindarin." Sindarin is, in fact, the conversational version, while Quenya is the ceremonial one.

Neither of the two forms of Elvish was originally designed as a speakable language. Quenya has a large vocabulary but few grammar rules, while Sindarin has detailed grammar, but less vocabulary. It is still possible to become quite fluent, however, given these limitations - which is the point of the "Useful Elvish Phrases" section really!