Quenya is the High-tongue of Valinor, I believe.
Sindarin is the language that is more freely spoken in LotR.
Nandorin was the somewhat developed language of the NAndor.
Noldorin....not sure about that one.....
Doriathrin is the homeland tongue of Luthien Tinuviel.....
Avarin, language of the Dark Elves.....
Then theres Telerin, the language of the Teleri..........
There are rather like 8 or 10 different ones 😂 or more than a dozen when you also count the non-elvish ones, like Soval Phare, Adûnaic or Khazad
But as AE said, the only ones with a fully developed grammar, structure etc are Sindarin and Quenya.
While Quenya is rather the "dead" language in the Third Age and was nearly only used for ceremonical stuff in Middle-earth, Sindarin was still the primary language of the Dúnedain and also used for names there.
Unlike most "artificial" fantasy languages, those two also have a real "character" and are quite different from each other, though they both have the same roots - Quenya is calm, noble and sounding kingly, a little cold as there are fewer voiced sounds than in Sindarin etc.
There is a lot of structural grammar, especially for the nouns (10 different cases, hence often compared to Finnish),
While in Sindarin the grammar mostly concerns the phonological details, like consonantal mutations or vowel assimilations (like the european "umlaut"-phenomenon).
Most people say Sindarin is easier, I don't think so though - in Sindarin, there are a lot of things you have to understand which often takes ages and still doesn't explain everything while in Quenya, there are more things that could also be found in practical tables; there are also less possibilities for misunderstandings I think, but because of the long words it simply looks more difficult than it imo is.
If you really want to learn it - here some courses:
http://home.agh.edu.pl/~evermind/mathom/quetin_lambe_eldaiva_en_part1.zip (Quenya)
http://home.agh.edu.pl/~evermind/mathom/pedin_edhellen_en.zip (Sindarin)
http://www.uib.no/People/hnohf/qcourse.htm (another Quenya one, but more detailed and complicated)
edit
as usually too late 😛
Easiest? Hm... maybe... I still think it's harder than Quenya, with all the consonant mutations, especially as there are so many exceptions for everything... Quenya is kinda... more regular. Maybe I also just think so because I havent spent too much time with Quenya etymology 😛
Originally posted by Sauron
I know the one remaining sentence of water elvish 🙂*bubble bubble*
which i already stated means 'wow, saurons great ring of power'