- Well, Quenya and Sindarian both come from a prior language.
Qyenya did influence Sindarian, especially in areas where a number of
Noldor settled after Feonor came back to Middle Earth, and then later
fell. Especially after many Sindarians heard of the kin slaying and then
other acts of violence by Noldor (one of the groups that spoke Quenya?
Vanya? and Teleri (related to the Sindarians genetically) in their quest
to get back the Silmarillions and bring Melkor/Morgoth down.
Though the Noldor are the ones who brought back the act of writing it
seems to middle earth. Feonor being the one who invented the Tengwar,
sort of based on an earlier script by Rumil?
Basically the Noldor exiles started using Sindarian, but with an accent.
Cause their own language was often looked on as hated by Sindarians. Kin
slaying, where many Teleri (kin to those who speak Sindarian, but in the
undying lands), cause the Noldor wanted their boats. While many Noldor
went up and over the top of the world to arrive in Middle Earth later.
Boats that were later destroyed by Feonor, Feonor the father of
Galadriel (it says much of why she had the test of power, when she was
offered the ring, for she know more than any immortal, the agony of the
fight against Sauron. Sauron the chief lieutenant of Melkor/Sauron,
Morgoth the one who stole the Silmarillion, helped kill the one tree,
and pool. And killed Galadriels grandfather in the process.
Much of the above, is from memory and it has been a while since I read
much of Quenya in a while, and its history.