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Origins and family
Taliska was not related to the Haladin tongue, at all therefore when the Númenóreans returned to Middle-earth in the Second Age, they did not recognise the peoples of Enedwaith and Minhiriath as their distant kin, who spoke unrelated languages.
Adûnaic was generally considered to be a language of less prestige than the Elven tongues. Thus most important documents and maps of Númenor, and most of the lords and ladies of the Dúnedain, used Quenya or Sindarin names instead of Adûnaic ones. Even most commoners knew Sindarin to some degree.
Most of the House of Bëor had been killed after the Dagor Bragollach, but even during the Second Age a Bëorian accent of Adûnaic still survived in parts of Númenor, most notably in Emerië and around the harbour of Andúnië.
Days of Pride
About 2,000 years into the Second Age, the Númenóreans began to envy the immortality of the Firstborn, which extended to the languages of the Elves; the Kings their followers, used the Elven tongues less and less. Though the Kings and Queens had all taken their names in Quenya, after some time their supporters used their Adûnaic names to refer to them.
Eventually Ar-Adûnakhôr took his name in Adûnaic and forbade anyone to speak the Elven tongues in his presence. The supremacy of Adûnaic was most strongly enforced by Ar-Gimilzôr: he outlawed the use of Elvish anywhere in Númenor, which antagonized the few Faithful Númenóreans still living in the land.
However, his son Inziladûn took a Quenya name again, Tar-Palantir, repealed the ban on the Elven tongues and gave peace to the Faithful. His daughter Míriel would probably have continued his reforms, but her cousin Pharazôn seized power and, in addition, gave her an Adûnaic name (Ar-Zimraphel).
With the Downfall of Númenor came the end of classical Adûnaic. The study and preservation of the language was neglected by the Exiles of Númenor, because they associated it with the rebellious and repressive Númenórean Kings.
However, the Men of Middle-earth who descended from the early Númenórean sailors and colonists still spoke it as a Common Speech. This language eventually evolved into the Westron tongue widely spoken during the Third Age.