Grand Ages: Medieval
50 Achievements
GOG
Producer
Out of all your competitors, you built the most businesses upon reaching the rank of "Emperor".
5.5%
How to unlock the Producer achievement in Grand Ages: Medieval - Definitive Guide
NemoG
GLITCHED
This glitched on me in my first sandbox game, I did have the biggest town and the most businesses but only the Cosmopolitan City trophy popped for me, though it did pop during my second game. I'm not sure why it glitched.
By the time you reach the rank emperor you'll need to be the one with the most businesses. When you press the 
button, you can see who has the most businesses in the current game so make sure you're at the top by the time you're King. The trophy will pop when you hit Emperor.