I'm not an experienced reverse engineer by any means but I took a peek at dwarf fortress in IDA and found what I believe is the combat simulation function. At least it uses strings like: "flies off in an arc" and concatenates them together.
The function itself is massive, I had to increase the node limit for IDA graph view to see it in graph mode. If rest of the code base is similar then I can see how it would be a big job to untangle it all and parallelize.
Tarn has also said that he is not a SW developer, coding is just means to an end for him to make a game so I sort of expected spaghetti.
The game is great though!