Imaginary languages are now par for the course in fantasy literature: sometimes called something like 'the old tongue' or 'the ancient language', sometimes the languages of different types of being or of people living in different places. In many cases these languages aren't developed beyond a few words (e.g. in The Wheel of Time, The Chronicles of Thomas Covenant, or A Song of Ice and Fire), but some authors have actually constructed whole languages for the purposes of a single work of fiction: e.g. the language of Klingon was invented for Star Trek, and for the Game of Thrones TV series, a linguistics expert was employed to create the Valyrian and Dothraki languages. I suspect Christopher Paolini has invented more than just the phrases listed at the end of each book for his elvish and dwarvish tongues, but I haven't seen this confirmed. Tolkien was already devising his own languages as a young boy, and continued to do so throughout his life, so it makes sense ...