Well, for some of the songs you can find some loosely translated lyrics and such.
The songs tend to be written in either some pseudo-Latin language (i.e it looks like Latin, but it's a little self-made here and there) or in one of Blizzard's own languages for the in-game races (Thalassian, the Blood Elves language, for the Lament of the Highborne song for example).
Anyway, here's a few (if you search around a bit on the web you can probably find some more attempted translations for various songs :P):
A Call to Arms:
O Thanagor (part of Invincible, Arthas, My Son, and other Lich King pieces):
Lament of the Highborne:
The Lament of the Highborne got a Night Elf version with Cataclysm, called Nightsong, which basically tells the story of the Night Elves the same way as Lament of the Highborne tells the story of the Blood Elves (it's on the Cataclysm soundtrack, and Russell Brower talks a bit about it on the Behind the Scenes DVD if you own that :P):
Here's the sort-of agreed upon lyrics for Nightsong (in Darnassian):
I won't dare to post a translation to this as it's still debated a bit here and there. Some of it you can guess yourself. Like Quel'dorei means Highborne, and Nordrassil is the world tree, and so on.
Anyway, there are of course a lot more songs and lyrics, but ultimately, you have to toy a bit with Blizzard's languages yourself, and make some qualified guessing, in order to get a translation (since Blizzard themselves seem quite reluctant with releasing their lyrics :P).
Anyway, here's the "old" encyclopedia to Darnassian:
And then for the Stormwind theme I'm a bit clueless, lol :/
It sounds Latin, but I'm no huge expert there so it can just as well be random syllables that just come across as being some fancy language, but which really is pure gibberish. A good non-Warcraft example of that is the soundtrack for Gladiator, the track called "Now We Are Free". It sounds really beautiful, but it's pure gibberish :P
Anyway, what I actually actually wanted to say, was that Blizzard teamed up with Alfred Music Publishing not long ago, in order to publish the sheet music for a lot of the World of Warcraft music. Initially it was just the nodes, but lately they've started to include the vocal lyrics to some of the sheet music as well, which is the (non-translated) official lyrics :P
You can find it all here:
And that is probably the page you have to keep an eye on, because if Blizzard were to release the lyrics for the Stormwind music, then it will probably be released there.
Edited by Jito on 09/05/2011 20:04 BST