How does Earendil speak Beorian?

[Galadriel55]

Originally Posted by Galin

A note adds that the Halethian language was already failing before Turin's time, and finally perished after Hurin in his wrath destroyed the small land and people.

How was the language failing? Just that the number of speakers was dwindling? Or the language was becoming too dilute and polluted with the additions of all the refugees fleeing to Brethil after the Nirnaeth?