I'm not sure if any of the strategic AI is exposed in civ4, but reading about that game I'd guess it wouldn't be of any use anyway, and the same for civ5, since if the goal of "prestige" is nothing that exists already, though one possibility is to only allow a UN victory, so whoever is most popular at the end wins. In civ4 I think everyone would be eligible, whereas in civ5 there would only be the USA and USSR as civs, and then a bunch of city states (CS) which are not eligible, though they do vote.
There is lots of code available for things like moving units around in civ4. This can be done in python, or C++. There are functions for adjusting the attitudes, and declaring war/peace/vassal, etc. So whatever is available, it's all there now, and probably someone has done something similar so there are examples available.
As for the same richness being available in civ5.. you should look over:
http://wiki.2kgames.com/civ5/index.php/Lua_Game_Objects
Not all of the same functions are available (yet?), and when that will change is unknown. The original announcement about the SDK coming was 6 months ago, and the latest news only said it won't be in the next release.
Whichever you choose you'll probably end up with a bunch of custom code that does all the work. By using a random number along with some modifiers and a range of thresholds... AI(close enough anyway)! And if you went with the UN and your code just modified the attitudes, then either should work, so long as all the necessary Lua functions exist. If they do then you could create a tiny mod. It would have a map, and then the custom Lua code.