If I remember correctly Civ4 originally launched with a python based AI, but they had to put it back into the C++ and everyone was thankful. The time between turns was absoutely brutal. You could hit the end turn button and go run errands before your next turn started. The end game was pretty much unplayable. Python does entail a performance hit. No doubt about it. If you want to get fancy with the AI, python might be a hindrance.
Thankfully, we had access to the Civ4 C++ source code, so we could still do AI modding.
I am surprised python could have crippled AI performance so much. It's not that slow.
Furthermore, python's syntax is very smart and easier to learn for people.
It's a full langage, not only a scripting one.