The phrase "a mastery of language" is correct and usable in written English.
It can be used to describe someone who has a high level of skill or proficiency in using language effectively.
Example: "Her poetry reflects a mastery of language that captivates readers and evokes deep emotions."
Alternatives: "a command of language" or "an expertise in language".
Indeed, summarizing text perfectly would require genuine intelligence, including commonsense knowledge and a mastery of language.
As Richard II nears dethronement, he attains a mastery of language that stuns the audience.
What was notable in all the writing, above and beyond a mastery of language and of storytelling, was a palpable sense of ambition.
He came slowly to a mastery of language, form, and style that revealed a mind like a solar system, with abstract ideas orbiting a radiant lyricism.
"What was notable in all the writing, above and beyond a mastery of language and of storytelling, was a palpable sense of ambition," the New Yorker editors note in the introductory essay explaining their choice of writers.
Not only did pictorial fancies without precedent flow lightly and freely, but Max Ernst turned out to have a mastery of language that was never to desert him, whether in German or in French.
Moreover, a mastery of languages is not the only accomplishment that every child might like to have when leaving school, or even the only one that society might like to bestow upon those it tries to educate.
His verse is characterized by a precise command of language and a mastery of lyric, dramatic, and meditative poetic forms.
The persuasive genius of Frederick Douglass, of Abraham Lincoln, of Ida B. Wells, of Cesar Chavez, sprang from a mastery of this language, and a perception of its application to a previously unimaginable future.
One continues to stand out above the rest: Montaigne's "Essays". I suppose he is even better in French, at least for those with more of a mastery of the language than mine.
The dream-link lyricism of the songs is packed with energetic imaginings and wonderfully absurd juxtapositions with hilarious ramblings from the band interspersed between them showing a mastery of the language of nonsense and the abstract.
