The languages in LotR are all Tolkien's creation. The two most developed are Quenya and Sindarin are the two most developed, thus are the most talked about, but he also created at least 20 different languages. Sadly, most of his linguistic papers haven't been published, and therefore are probably in his son's posession, or lost.
But yeah, Tolkien's work is legit. He loved language and studied that crap as an early child. In fact, the reason he wrote in the first place was to give an excuse for the existence of his languages.
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