Usage examples "idiomatic":
The minuteness of his observation, the keenness of his perception of all these things, give him a real originality which is confirmed by a style sometimes indeed idiomatic
and unfinished to a fault, but capable of remarkable felicity and vividness. - "Views and Reviews",
Gustavus Weitbreck had lived so long on his Pennsylvania farm that he even thought in English instead of in German, and, strangely enough, in English much less broken and idiomatic
than that which he spoke. - "Between Whiles",
Helen Hunt Jackson.
Not only could he speak most of the languages of the East, including Arabic and Persian, but he wrote good idiomatic
English. - "The Life of Sir Richard Burton",