I'm an American student (native English speaker), and I've never heard "take a decision before."

English is a lot less formal in spoken form than written, even if it's sometimes incorrect. It kind of distracts the viewer if the Big Bad suddenly says, "Whom did you kill?" Sometimes I watch movies and I just think "No, I would never tell English-learners to see this in order to improve their language skills."

Just as a commentary on how it "feels" now to say "hey" instead of "hello," the first is much more casual compared to the second. I would feel slightly stilted saying "hello," to anyone that I know casually. In interviews, I would either say "Hi," "Hello," or "How are you?" as a greeting. "Hey" seems coarser, like "What's up?"