Translation

I want to translate this into both Sindarin and Quenya:

I will love you until this world is forgotten and crumbled beneath the stars, and after.

Would (thaquet-) work for I will?

No, the meaning of thaquet- is "to agree with something, agree to do something", so it is "I will" in the sense of "Will you come to the cinema tomorrow?" "I will".

The "I will" in your sentence is expressed in Quenya or Sindarin by conjugating the verb "love" in the future tense.

For Quenya, here is my transcription: "Meluvanyë lyë tenn' ambar sina vanw' ar taltaina nu i eleni ná, ar apa." Note that i changed Forgotten (*Etsenina (?)) for "Vanwa" (Gone, over, passed away), it just seemed better to me + i don't realy know how valid "etsen" actually is, but change it if you will, i also suggest "hessa" that stands for withered.

Thanks!