I am not a linguist (although I took some grad classes in phonological analysis and theory of language), but I have some questions.
As far as I know Sapkowski's elven language is very incomplete. Words and sentences were made up to satisfy his literary needs, and not the other way around. So who adds official words to Sapkowski's elven? Have the RED's added any for their own convenience? Has the lyricist created words? If so we might as well never know their meaning, unless he/she kindly provides it to us.
Also, do we have any knowledge of formal grammatical rules of Sapkowski's elven? Or are we just assuming that, due to other similarities, it borrows its grammar from Gaelic or whatever other language it is based on? This could actually simplify things, as all Indoeuropean languages share the same general structure.
And finally, vocabulary and referential words and phrases. Have you guys read any medieval or older literature? Take for instance the literary figures in the Elder Edda. They talk about things we can imagine, like storms and wolves, in ways we have a hard time understanding, because to them they meant something different than what they mean to us. Languages and words are referential, they are not opaque like a sentence in first order logic. Chances are the words and phrases contained in this so far cryptic elven are known to us, but, if the writer was creative enough, these things might as well translate to something wild and chaotic without any concrete meaning (to us).
Just some thoughts. Now let the translation begin