We also use could to say that somebody had the general ability or permission to do something: My grandfather could speak five languages.

My grandfather spoke a language so obscure that even a symbologist can't identify it?

It had really been necessary at that time, since grandfather and grandmother spoke exclusively in wolvish.

"When my grandfather spoke of the bank," he used to say, "we usually observed a moment of silence."

I understand that Alex and his grandfather speak Russian through most of the film.

She had never heard her grandfather speak in anything other than calm tones.

My mother used to tell me that my great-great-great grandfather actually spoke to one of the gods who lived under the ground.

He stood on the seashore way up north, in winter, and he heard his grandfather speak to him clear as a bell.

My grandfather doesn't speak a word of English, but he manages to do all his shopping, and somehow communicate with the people around him nevertheless.

He tells how his grandfather spoke Yiddish to the farm animals, who "understood him very well."