If I want to read Tolkien's text aloud, or appreciate the rhythm and rhyme in his poems, I find it distracting not to know how names including these characters (and similar ones) were meant to be pronounced. Unfortunately I only have the main books in e-book format; if this is answered in some background material I would highly appreciate a summary or even a literal quote thereof.
I am in particular interested in these letters, from which I assume it would be more or less straightforward to generalize to others reusing the same accents:
ä (e.g. Eärendil): I suspect umlaut (German) or separation of sounds (French) or both, but I'm having a hard time in making the first verse trochaic (in accordance with the rest of the poem) in
Eärendil was a mariner
that tarried in Arvernien;
he built a boat of timber felled
in Nimbrethil to journey in [...]
û (e.g., Nazgûl or Khazad-dûm): I'm pretty sure that this is just the sound I know as "u" (sounds like the /oo/ in /doom/):
The shadow lies upon his tomb
In Moria, in Khazad-dûm.
What's the difference to "u" then?
é (e.g., Sméagol or Éoden): here I only have the pronunciation they adopted in the movie adaptation, the problem of which is that it plainly ignores any diacritics and says "Smeagol" in English pronunciation. I very much doubt that is what was intended. Similarly to the above, how to differentiate "é" from "e"?