How to say “The first company would finish by September, whereas the second company wouldn't finish until December.” in Japanese
In Japanese
一つ目の会社は九月までに終わるのに対して、二つ目の会社は十二月まで終わりません。
Hitotsume no kaisha wa kugatsu made ni owaru no ni taishite, futatsume no kaisha wa jūnigatsu made owarimasen.