Having to write the same logic twice in two languages, and then making sure both implementations behave the same way. I don’t know if I’d use the word “barrier”

Having to write the same logic twice in two languages, and then making sure both implementations behave the same way. I don’t know if I’d use the word “barrier”, it’s certainly a significant pain in the ass. The classic example is of course validation, but plenty of other places it can come up.