Here is the full list of all 50 Lethis - there are Path of Progress achievements.
You’ve listened to 100 pedestrians, in all your cities together.
A pirated copy of the game has been detected. But you bought the game, so you’re forgiven.
You completed the campaign on maximum difficulty.
You Completed the campaign on “normal” difficulty or harder.
You completed the campaign on “easy” difficulty or harder.
You completed the epilogue (Chapter XXVI)
You completed part five (Chapters XXI to XXV)
You completed part four (Chapters XVI to XX)
You completed part 3 (Chapters XI to XV)
You completed part two (Chapters VI to X)
You completed Chapter IX
You completed part one (Chapters I to V)
You completed a mission without cutting down trees or bushes (outside tutorial missions).
You've exported a total of 100.000 units of silk, all cities together.
You’ve built 50 Automaton factories, all cities together.
You’ve built 25 steam-powered buildings during one game.
You've exported 100.000 units of alcohol (Absinthe or beer), all cities together.
You cut down 50 trees during a game.
You destroyed 1.000 buildings, all cities together.
You built the four monuments during a sandbox game.
Unlock the Winter garden, Summer sky, Springtime science and Autumn flight achievements.
You’ve finished building the Botanical Garden during winter.
You’ve finished building the Zeppelin Hangar during autumn.
You’ve finished building the Observatory during summer.
You built a monument, only to destroy it right away (And boy, did it hurt !)
You’ve finished building the World Exposition during spring.
You entered a second valid cheatcode in the console.
Enter « Ambrosia » in the cheat console.
You’ve built 50 road blocks during one game.
You took time to watch the credits.
You took a screencap of the city you’re the most proud of.
You produced 20.000 units of fish and 20.000 units of potato during one game.
You captured 20.000 faes in one game.
You have 7 functioning mines in one city.
You built each type of farm during one game.
You completed the tutorial missions.
100 houses withered by time, all cities together.
You’ve built 5.000 buildings, all cities together (excluding roads, bridges and roadblocks).
You responded to 20 of the Emperor’s requests, all cities together.
500 houses have been exorcised, all cities together.
You built over 10.000 box tiles of road, all cities together.
You responded to 3 scientific requests during Chapter 24.
Your unemployment rate went over 50 % (with a population over 2000 inhabitants).
80.000 potatoes harvested in one harvest, congratulations !
You managed cities for ten hours.
You managed cities for fifty hours.
Finish a game while having experienced three revolts.
You’ve experienced a revolt during the month of Germinal.
You’ve witnessed your very first revolt.
You didn’t respond to 20 of the Emperor’s requests, all cities together.