In about a month’s time, I had made a tolerable proficiency in their language, and was able to answer most of the king’s questions, when I had the honour to attend him.
Four times a year the youth of a certain district meet to show their proficiency in running and leaping, and other feats of strength and agility; where the victor is rewarded with a song in his or her praise.
My master was eager to learn "whence I came; how I acquired those appearances of reason, which I discovered in all my actions; and to know my story from my own mouth, which he hoped he should soon do by the great proficiency I made in learning and pronouncing their words and sentences."
There are no more uses of "proficiency" in the book.
Show samples from other sources
Not as well as my mother, but I’m pretty proficient."
Kiera Cass -- The Heir
Yvette was by far the most competent of my coworkers, and she and I would often work together on any electrical job requiring proficiency with tools.