Númenórean,Adûnaic Biography Advice

[Aestivan]

Númenor was destroyed over three thousand years before the time of the game, in the previous Age. Adûnaic as a daily speech no longer exists as such, having long since changed with the years into Westron, the Common Speech. Dúnedain of the North and Men of Gondor who honored their Númenórean heritage took names in Sindarin (their kings took regnal names in Quenya). Adûnaic names were associated with the "King's Men" faction of Númenor under the influence of Sauron, who rebelled against the Valar. This is why Denethor, Faramir, Imrahil, Beregond, Finduilas and others in Gondor have Sindarin names.

I recommend you at least read the Allakabêth, the chapter of The Silmarillion that gives an account of Númenor and its fall. You might also read "Appendix A" to The Return of the King for an account of the aftermath, the War of the Last Alliance, and the later history of Arnor and of Gondor. For insight into the matter of language, I also recommend the essay "Of Dwarves and Men", published in The History of Middle Earth, Vol XII: The Peoples of Middle Earth, by Christopher Tolkien.