I can't speak for Tolstoy, but the Gutenberg version of Dostoevsky was atrocious compared to the Pevear & Volokhonsky translation. FOr a more modern example, Simone de Beauvoir's first translation was by an unskilled botanist who happened to know french and english. A recent translation came out that is night and day compared to the original, but it will enter public domain some fifty years later.