ost certainly they were, especially the Elven languages Sindarin
and Quenya. "[These were] no arbitrary gibberish but really possible
tongues with consistent roots, sound laws, and inflexions, into which
he poured all his imaginative and philological powers..." (Obituary,
in Scholar, p. 12). Furthermore, they were both derived from a
"proto-Elvish" language, again in a linguistically realistic manner.
(Sindarin was the "everyday" elvish language while Quenya was a kind
of "elf-latin"; therefore, most Elvish words in LotR were Sindarin.
Examples: most "non-English" place-names on the
map (e.g. Minas Tirith, Emyn Beriad) were Sindarin, as was the song
to Elbereth sung in Rivendell; Galadriel's lament was in Quenya.)The language of the Rohirrim was a real language: Anglo-Saxon (Old English), just as their culture (except for the horses) was that of the Anglo-Saxons. (It was, however, not the "standard" West Saxon Old English but rather the Mercian equivalent (RtMe, 94).) Most of the other languages in LotR were much less fully developed: Entish, Khudzul (Dwarvish) and the Black Speech (the language of Mordor, e.g. the Ring inscription). Adunaic, the language of Númenor, developed in 1946 while he was finishing up LotR, was said to be his fifteenth invented language.