For instance, the transliterations they do on the site are wrong. The "r" that looks like a "y" is actually used for a trilled r and the other r is used for everything else. Lynne doesn't have a double letter in it because the n isn't pronounced twice, as it is in something like "penknife". And the e isn't ponounced at all. Also, the dots for the y are only used when you palatalize a consonant, using the "y" as a consonant as well (like in "Tanya"). If the y is a vowel, than you just use the symbol for the vowel sound it's cinema for adult viewingouned as. And the dot is never used for e, silent or otherwise, and all the vowels can be written either above or below.
Tolkien worked on that language for his entire life, that's how it's so detailed. Also, he was a professor of languages, so he most likely derived it from Sanskrit. And he probably adapted it to Quenya and Sindarin, which are based on Finnish and Welsh, respectively.
This isn't a language, it's a writing system. And Quenya is also based off of Latin. There is actually a Quenya Mode of Tengwar, and a Sindarin Mode, and also an English Mode which is a little short of vowels however, which is what makes it a little confusing. But it's nothing like what this site claims it is. It was meant to be a way to phonetically represent words in any language for which there was a Mode, not a way to simply encode the letters of that language or be a language in and of itself.