Souperviel
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Regarding building two structures in one city per turn, as far as I know, it's impossible. You can only create some kind of workaround trigger and use it to script the construction of any number of buildings per turn, be it 2, 10, or more.
That's a shame; I'd like this feature to be implemented for the AI as well, but it seems it won't be able to utilize it.
I wonder which file contains the building bonuses.