How would you know?

[Findegil]

Were would AElfwine go? And what would he learn there?

If he still came to Eressea it is most probably a kind of a Silmarillion that he brought back and not the story of the War of the Ring.

So what might Tolkien have owned to translate?

Probably he had a complete copy of the Red Book, including the volumes of 'Translaions from Elvish' that Bilbo made in Rivendell in Westron and in some kind of elvish script. In addition he might have had a 'Silmarillion' from AElfwine in Old English. Thus he could translate the later and gain some insight into elvish languages simply by the names and some battle cries and so on perserved by AElfwine. Now seeing the similarty of the story given in Bilbos translations to what he had got from AElfwine the good Professor together with his professional konwledge about languages probably was able to transscibe and translate what he found in the Red Book.

It does'nt seems to me so much harder than egyptian hyroglyphs.

Respectfuly
Findegil