Wiktionary
unidiomatic
a. Not idiomatic.
Usage examples of "unidiomatic".
And the remedy is as simple as the diagnosis: the artist must penetrate his work, wrap it around him, give it the distilled, unique essence of his heart and mind, so that it will blaze up and reveal his soul, even through the veil of unidiomatic technique.
He feels that you should adhere as closely as possible to the English text without making your translation so literal as to be un-German and unidiomatic, and therefore not very readable to German-speaking people.