But E. Coli does use the same chart as humans, so E. Coli understands the recipe exactly the same way that a human does, and therefore the E. Coli does make human insulin from the recipe, just as the genetic engineers expect it to. The recipe for every single living organism is written in exactly the same language. This is an essential prediction of evolution. If this were not true, eventually the genetic engineers would notice because one of their experiments in genetic modification would fail because the DNA sequence they've programmed will be interpreted wrong. But that's never happened.
Evolutionary theory predicts that everything alive uses the same chart.
Every time they do so, they're testing Evolution and proving that it is true. If anyone ever finds an organism here on earth whose encoding chart is completely different than the one we know now, and as I mentioned there's an astronomically large number of possible encoding charts, someone's going to have a lot of explaining to do. But that's never happened. Every living organism which has ever been checked has turned out to use exactly the same translation chart as every other living organism. That's a very strong prediction of evolutionary theory, and the fact that genetic engineers are using that prediction as part of their engineering, and getting the right answer because they do so, is a very strong test and confirmation of evolutionary theory.